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 $67.37   13.221%   $76.277   $76.28   $76.30   $76.30  
  Purchase #2 $192.81   12.370%   $216.6606   $216.66   $216.65   $216.70  
  Purchase #3 $214.27   6.253%   $227.6683   $227.67   $227.65   $227.70  
  Purchase #4 $192.27   6.366%   $204.5099   $204.51   $204.50   $204.50  
  Purchase #5 $160.76   11.639%   $179.4709   $179.47   $179.45   $179.50  
  Purchase #6 $221.57   8.398%   $240.1774   $240.18   $240.20   $240.20  
  Purchase #7 $241.43   10.759%   $267.4055   $267.41   $267.40   $267.40  
  7 purchase totals = $1,290.48       $1,412.1696   $1,412.18   $1,412.15   $1,412.30