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 $199.54   4.849%   $209.2157   $209.22   $209.20   $209.20  
  Purchase #2 $24.43   6.267%   $25.961   $25.96   $25.95   $26.00  
  Purchase #3 $74.37   3.295%   $76.8205   $76.82   $76.80   $76.80  
  Purchase #4 $9.75   6.539%   $10.3876   $10.39   $10.40   $10.40  
  Purchase #5 $195.29   5.724%   $206.4684   $206.47   $206.45   $206.50  
  Purchase #6 $250.34   6.648%   $266.9826   $266.98   $267.00   $267.00  
  Purchase #7 $155.64   10.306%   $171.6803   $171.68   $171.70   $171.70  
  7 purchase totals = $909.36       $967.5161   $967.52   $967.50   $967.60