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 $32.29   3.417%   $33.3933   $33.39   $33.40   $33.40  
  Purchase #2 $216.88   5.354%   $228.4918   $228.49   $228.50   $228.50  
  Purchase #3 $215.58   7.701%   $232.1818   $232.18   $232.20   $232.20  
  Purchase #4 $56.48   7.325%   $60.6172   $60.62   $60.60   $60.60  
  Purchase #5 $235.78   4.115%   $245.4823   $245.48   $245.50   $245.50  
  Purchase #6 $24.89   6.759%   $26.5723   $26.57   $26.55   $26.60  
  Purchase #7 $58.67   3.776%   $60.8854   $60.89   $60.90   $60.90  
  7 purchase totals = $840.57       $887.6241   $887.62   $887.65   $887.70