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 $176.72   13.440%   $200.4712   $200.47   $200.45   $200.50  
  Purchase #2 $94.78   10.516%   $104.7471   $104.75   $104.75   $104.70  
  Purchase #3 $158.30   12.184%   $177.5873   $177.59   $177.60   $177.60  
  Purchase #4 $150.63   13.362%   $170.7572   $170.76   $170.75   $170.80  
  Purchase #5 $163.88   8.696%   $178.131   $178.13   $178.15   $178.10  
  Purchase #6 $34.92   12.813%   $39.3943   $39.39   $39.40   $39.40  
  Purchase #7 $178.87   8.154%   $193.4551   $193.46   $193.45   $193.50  
  7 purchase totals = $958.10       $1,064.5432   $1,064.55   $1,064.55   $1,064.60