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 $146.61   13.156%   $165.898   $165.90   $165.90   $165.90  
  Purchase #2 $141.66   5.685%   $149.7134   $149.71   $149.70   $149.70  
  Purchase #3 $12.52   13.770%   $14.244   $14.24   $14.25   $14.20  
  Purchase #4 $200.82   13.540%   $228.011   $228.01   $228.00   $228.00  
  Purchase #5 $97.91   12.293%   $109.9461   $109.95   $109.95   $109.90  
  Purchase #6 $89.87   12.358%   $100.9761   $100.98   $101.00   $101.00  
  Purchase #7 $77.45   5.122%   $81.417   $81.42   $81.40   $81.40  
  7 purchase totals = $766.84       $850.2056   $850.21   $850.20   $850.10