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 $204.39   10.608%   $226.0717   $226.07   $226.05   $226.10  
  Purchase #2 $140.36   8.532%   $152.3355   $152.34   $152.35   $152.30  
  Purchase #3 $237.40   7.578%   $255.3902   $255.39   $255.40   $255.40  
  Purchase #4 $197.74   7.552%   $212.6733   $212.67   $212.65   $212.70  
  Purchase #5 $157.78   6.828%   $168.5532   $168.55   $168.55   $168.60  
  Purchase #6 $193.98   4.717%   $203.13   $203.13   $203.15   $203.10  
  Purchase #7 $140.38   8.700%   $152.5931   $152.59   $152.60   $152.60  
  7 purchase totals = $1,272.03       $1,370.7470   $1,370.74   $1,370.75   $1,370.80