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 $249.43   10.669%   $276.0417   $276.04   $276.05   $276.00  
  Purchase #2 $45.46   6.834%   $48.5667   $48.57   $48.55   $48.60  
  Purchase #3 $32.36   13.789%   $36.8221   $36.82   $36.80   $36.80  
  Purchase #4 $174.62   7.106%   $187.0285   $187.03   $187.05   $187.00  
  Purchase #5 $204.27   12.589%   $229.9856   $229.99   $230.00   $230.00  
  Purchase #6 $185.57   9.271%   $202.7742   $202.77   $202.75   $202.80  
  Purchase #7 $70.87   5.861%   $75.0237   $75.02   $75.00   $75.00  
  7 purchase totals = $962.58       $1,056.2425   $1,056.24   $1,056.20   $1,056.20