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 $95.88   6.367%   $101.9847   $101.98   $102.00   $102.00  
  Purchase #2 $22.52   6.378%   $23.9563   $23.96   $23.95   $24.00  
  Purchase #3 $111.47   4.751%   $116.7659   $116.77   $116.75   $116.80  
  Purchase #4 $140.99   3.829%   $146.3885   $146.39   $146.40   $146.40  
  Purchase #5 $152.57   4.477%   $159.4006   $159.40   $159.40   $159.40  
  Purchase #6 $181.87   10.457%   $200.8881   $200.89   $200.90   $200.90  
  Purchase #7 $84.36   3.765%   $87.5362   $87.54   $87.55   $87.50  
  7 purchase totals = $789.66       $836.9203   $836.93   $836.95   $837.00