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 $60.87   4.392%   $63.5434   $63.54   $63.55   $63.50  
  Purchase #2 $159.29   7.822%   $171.7497   $171.75   $171.75   $171.70  
  Purchase #3 $62.57   4.197%   $65.1961   $65.20   $65.20   $65.20  
  Purchase #4 $246.75   8.278%   $267.176   $267.18   $267.20   $267.20  
  Purchase #5 $42.68   6.142%   $45.3014   $45.30   $45.30   $45.30  
  Purchase #6 $48.95   6.515%   $52.1391   $52.14   $52.15   $52.10  
  Purchase #7 $125.77   6.155%   $133.5111   $133.51   $133.50   $133.50  
  7 purchase totals = $746.88       $798.6168   $798.62   $798.65   $798.50