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 $89.82   6.144%   $95.3385   $95.34   $95.35   $95.30  
  Purchase #2 $154.59   5.760%   $163.4944   $163.49   $163.50   $163.50  
  Purchase #3 $96.71   3.593%   $100.1848   $100.18   $100.20   $100.20  
  Purchase #4 $67.41   12.470%   $75.816   $75.82   $75.80   $75.80  
  Purchase #5 $46.88   7.748%   $50.5123   $50.51   $50.50   $50.50  
  Purchase #6 $124.27   5.313%   $130.8725   $130.87   $130.85   $130.90  
  Purchase #7 $144.29   9.329%   $157.7508   $157.75   $157.75   $157.80  
  7 purchase totals = $723.97       $773.9693   $773.96   $773.95   $774.00