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 $100.55   7.828%   $108.4211   $108.42   $108.40   $108.40  
  Purchase #2 $171.80   10.314%   $189.5195   $189.52   $189.50   $189.50  
  Purchase #3 $197.86   7.599%   $212.8954   $212.90   $212.90   $212.90  
  Purchase #4 $18.39   13.385%   $20.8515   $20.85   $20.85   $20.90  
  Purchase #5 $27.98   10.636%   $30.956   $30.96   $30.95   $31.00  
  Purchase #6 $102.64   10.749%   $113.6728   $113.67   $113.65   $113.70  
  Purchase #7 $225.86   5.770%   $238.8921   $238.89   $238.90   $238.90  
  7 purchase totals = $845.08       $915.2084   $915.21   $915.15   $915.30