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 $119.58   4.259%   $124.6729   $124.67   $124.65   $124.70  
  Purchase #2 $180.65   12.121%   $202.5466   $202.55   $202.55   $202.50  
  Purchase #3 $12.66   13.335%   $14.3482   $14.35   $14.35   $14.30  
  Purchase #4 $189.64   13.102%   $214.4866   $214.49   $214.50   $214.50  
  Purchase #5 $138.87   11.546%   $154.9039   $154.90   $154.90   $154.90  
  Purchase #6 $202.84   13.402%   $230.0246   $230.02   $230.00   $230.00  
  Purchase #7 $67.38   11.316%   $75.0047   $75.00   $75.00   $75.00  
  7 purchase totals = $911.62       $1,015.9875   $1,015.98   $1,015.95   $1,015.90