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 $48.49   5.413%   $51.1148   $51.11   $51.10   $51.10  
  Purchase #2 $225.93   8.667%   $245.5114   $245.51   $245.50   $245.50  
  Purchase #3 $176.72   3.183%   $182.345   $182.35   $182.35   $182.30  
  Purchase #4 $62.31   4.578%   $65.1626   $65.16   $65.15   $65.20  
  Purchase #5 $213.68   4.584%   $223.4751   $223.48   $223.50   $223.50  
  Purchase #6 $165.68   5.238%   $174.3583   $174.36   $174.35   $174.40  
  Purchase #7 $8.75   4.426%   $9.1373   $9.14   $9.15   $9.10  
  7 purchase totals = $901.56       $951.1045   $951.11   $951.10   $951.10