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 $228.86   11.710%   $255.6595   $255.66   $255.65   $255.70  
  Purchase #2 $64.54   12.845%   $72.8302   $72.83   $72.85   $72.80  
  Purchase #3 $32.65   6.295%   $34.7053   $34.71   $34.70   $34.70  
  Purchase #4 $235.83   3.825%   $244.8505   $244.85   $244.85   $244.90  
  Purchase #5 $46.37   5.605%   $48.969   $48.97   $48.95   $49.00  
  Purchase #6 $149.59   10.414%   $165.1683   $165.17   $165.15   $165.20  
  Purchase #7 $106.85   3.102%   $110.1645   $110.16   $110.15   $110.20  
  7 purchase totals = $864.69       $932.3473   $932.35   $932.30   $932.50