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 $55.57   12.393%   $62.4568   $62.46   $62.45   $62.50  
  Purchase #2 $229.68   5.180%   $241.5774   $241.58   $241.60   $241.60  
  Purchase #3 $24.96   6.104%   $26.4836   $26.48   $26.50   $26.50  
  Purchase #4 $53.64   6.327%   $57.0338   $57.03   $57.05   $57.00  
  Purchase #5 $126.28   8.248%   $136.6956   $136.70   $136.70   $136.70  
  Purchase #6 $201.55   3.834%   $209.2774   $209.28   $209.30   $209.30  
  Purchase #7 $103.78   13.536%   $117.8277   $117.83   $117.85   $117.80  
  7 purchase totals = $795.46       $851.3523   $851.36   $851.45   $851.40