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 $239.33   3.459%   $247.6084   $247.61   $247.60   $247.60  
  Purchase #2 $92.39   5.340%   $97.3236   $97.32   $97.30   $97.30  
  Purchase #3 $108.72   7.304%   $116.6609   $116.66   $116.65   $116.70  
  Purchase #4 $74.52   3.293%   $76.9739   $76.97   $76.95   $77.00  
  Purchase #5 $45.80   7.465%   $49.219   $49.22   $49.20   $49.20  
  Purchase #6 $236.36   4.621%   $247.2822   $247.28   $247.30   $247.30  
  Purchase #7 $62.46   5.459%   $65.8697   $65.87   $65.85   $65.90  
  7 purchase totals = $859.58       $900.9377   $900.93   $900.85   $901.00