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 $125.60   9.277%   $137.2519   $137.25   $137.25   $137.30  
  Purchase #2 $248.67   7.861%   $268.2179   $268.22   $268.20   $268.20  
  Purchase #3 $155.49   13.786%   $176.9259   $176.93   $176.95   $176.90  
  Purchase #4 $78.98   4.821%   $82.7876   $82.79   $82.80   $82.80  
  Purchase #5 $99.71   4.822%   $104.518   $104.52   $104.50   $104.50  
  Purchase #6 $28.79   10.544%   $31.8256   $31.83   $31.85   $31.80  
  Purchase #7 $236.39   11.351%   $263.2226   $263.22   $263.20   $263.20  
  7 purchase totals = $973.63       $1,064.7495   $1,064.76   $1,064.75   $1,064.70