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 $60.49   6.561%   $64.4587   $64.46   $64.45   $64.50  
  Purchase #2 $230.47   5.682%   $243.5653   $243.57   $243.55   $243.60  
  Purchase #3 $183.75   6.869%   $196.3718   $196.37   $196.35   $196.40  
  Purchase #4 $95.87   11.179%   $106.5873   $106.59   $106.60   $106.60  
  Purchase #5 $182.56   11.648%   $203.8246   $203.82   $203.80   $203.80  
  Purchase #6 $183.71   9.559%   $201.2708   $201.27   $201.25   $201.30  
  Purchase #7 $175.36   6.263%   $186.3428   $186.34   $186.35   $186.30  
  7 purchase totals = $1,112.21       $1,202.4213   $1,202.42   $1,202.35   $1,202.50