Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $204.26   4.827%   $214.1196   $214.12   $214.10   $214.10  
  Purchase #2 $127.35   8.593%   $138.2932   $138.29   $138.30   $138.30  
  Purchase #3 $225.27   6.788%   $240.5613   $240.56   $240.55   $240.60  
  Purchase #4 $156.55   11.179%   $174.0507   $174.05   $174.05   $174.10  
  Purchase #5 $219.87   8.110%   $237.7015   $237.70   $237.70   $237.70  
  Purchase #6 $119.35   5.689%   $126.1398   $126.14   $126.15   $126.10  
  Purchase #7 $244.43   11.802%   $273.2776   $273.28   $273.30   $273.30  
  7 purchase totals = $1,297.08       $1,404.1437   $1,404.14   $1,404.15   $1,404.20