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 $158.67   3.740%   $164.6043   $164.60   $164.60   $164.60  
  Purchase #2 $151.74   11.388%   $169.0202   $169.02   $169.00   $169.00  
  Purchase #3 $215.29   4.428%   $224.823   $224.82   $224.80   $224.80  
  Purchase #4 $102.37   8.105%   $110.6671   $110.67   $110.65   $110.70  
  Purchase #5 $45.67   13.828%   $51.9852   $51.99   $52.00   $52.00  
  Purchase #6 $67.48   4.117%   $70.2582   $70.26   $70.25   $70.30  
  Purchase #7 $212.66   4.590%   $222.4211   $222.42   $222.40   $222.40  
  7 purchase totals = $953.88       $1,013.7791   $1,013.78   $1,013.70   $1,013.80