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 $9.40   10.578%   $10.3943   $10.39   $10.40   $10.40  
  Purchase #2 $197.90   11.337%   $220.3359   $220.34   $220.35   $220.30  
  Purchase #3 $215.97   4.573%   $225.8463   $225.85   $225.85   $225.80  
  Purchase #4 $92.51   13.691%   $105.1755   $105.18   $105.20   $105.20  
  Purchase #5 $104.29   4.514%   $108.9977   $109.00   $109.00   $109.00  
  Purchase #6 $149.41   6.126%   $158.5629   $158.56   $158.55   $158.60  
  Purchase #7 $124.51   3.716%   $129.1368   $129.14   $129.15   $129.10  
  7 purchase totals = $893.99       $958.4494   $958.46   $958.50   $958.40