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 $55.94   5.164%   $58.8287   $58.83   $58.85   $58.80  
  Purchase #2 $167.46   9.844%   $183.9448   $183.94   $183.95   $183.90  
  Purchase #3 $41.88   7.428%   $44.9908   $44.99   $45.00   $45.00  
  Purchase #4 $133.68   8.146%   $144.5696   $144.57   $144.55   $144.60  
  Purchase #5 $68.33   8.635%   $74.2303   $74.23   $74.25   $74.20  
  Purchase #6 $216.86   12.750%   $244.5097   $244.51   $244.50   $244.50  
  Purchase #7 $5.85   11.456%   $6.5202   $6.52   $6.50   $6.50  
  7 purchase totals = $690.00       $757.5941   $757.59   $757.60   $757.50