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 $225.79   9.602%   $247.4704   $247.47   $247.45   $247.50  
  Purchase #2 $64.74   5.561%   $68.3402   $68.34   $68.35   $68.30  
  Purchase #3 $65.85   5.695%   $69.6002   $69.60   $69.60   $69.60  
  Purchase #4 $241.32   9.506%   $264.2599   $264.26   $264.25   $264.30  
  Purchase #5 $126.79   7.551%   $136.3639   $136.36   $136.35   $136.40  
  Purchase #6 $52.98   9.772%   $58.1572   $58.16   $58.15   $58.20  
  Purchase #7 $167.46   6.791%   $178.8322   $178.83   $178.85   $178.80  
  7 purchase totals = $944.93       $1,023.0240   $1,023.02   $1,023.00   $1,023.10