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 $68.45   13.274%   $77.5361   $77.54   $77.55   $77.50  
  Purchase #2 $183.49   11.435%   $204.4721   $204.47   $204.45   $204.50  
  Purchase #3 $173.95   5.620%   $183.726   $183.73   $183.75   $183.70  
  Purchase #4 $38.56   7.203%   $41.3375   $41.34   $41.35   $41.30  
  Purchase #5 $69.51   9.298%   $75.973   $75.97   $75.95   $76.00  
  Purchase #6 $28.52   10.388%   $31.4827   $31.48   $31.50   $31.50  
  Purchase #7 $154.97   3.140%   $159.8361   $159.84   $159.85   $159.80  
  7 purchase totals = $717.45       $774.3635   $774.37   $774.40   $774.30