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 $228.76   6.414%   $243.4327   $243.43   $243.45   $243.40  
  Purchase #2 $227.49   10.117%   $250.5052   $250.51   $250.50   $250.50  
  Purchase #3 $60.57   12.822%   $68.3363   $68.34   $68.35   $68.30  
  Purchase #4 $149.68   8.533%   $162.4522   $162.45   $162.45   $162.50  
  Purchase #5 $128.54   7.690%   $138.4247   $138.42   $138.40   $138.40  
  Purchase #6 $136.41   7.367%   $146.4593   $146.46   $146.45   $146.50  
  Purchase #7 $7.80   3.183%   $8.0483   $8.05   $8.05   $8.00  
  7 purchase totals = $939.25       $1,017.6587   $1,017.66   $1,017.65   $1,017.60