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   3.391%   $62.9341   $62.93   $62.95   $62.90  
  Purchase #2 $114.72   8.534%   $124.5102   $124.51   $124.50   $124.50  
  Purchase #3 $56.52   5.677%   $59.7286   $59.73   $59.75   $59.70  
  Purchase #4 $236.67   9.276%   $258.6235   $258.62   $258.60   $258.60  
  Purchase #5 $199.96   3.480%   $206.9186   $206.92   $206.90   $206.90  
  Purchase #6 $146.25   6.525%   $155.7928   $155.79   $155.80   $155.80  
  Purchase #7 $46.43   5.623%   $49.0408   $49.04   $49.05   $49.00  
  7 purchase totals = $861.42       $917.5486   $917.54   $917.55   $917.40