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 $44.45   13.325%   $50.373   $50.37   $50.35   $50.40  
  Purchase #2 $64.86   11.791%   $72.5076   $72.51   $72.50   $72.50  
  Purchase #3 $174.87   6.489%   $186.2173   $186.22   $186.20   $186.20  
  Purchase #4 $162.66   13.579%   $184.7476   $184.75   $184.75   $184.70  
  Purchase #5 $215.35   8.105%   $232.8041   $232.80   $232.80   $232.80  
  Purchase #6 $45.43   6.284%   $48.2848   $48.28   $48.30   $48.30  
  Purchase #7 $23.51   13.173%   $26.607   $26.61   $26.60   $26.60  
  7 purchase totals = $731.13       $801.5414   $801.54   $801.50   $801.50