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 $186.90   7.658%   $201.2128   $201.21   $201.20   $201.20  
  Purchase #2 $188.89   13.482%   $214.3561   $214.36   $214.35   $214.40  
  Purchase #3 $33.39   9.127%   $36.4375   $36.44   $36.45   $36.40  
  Purchase #4 $44.65   8.546%   $48.4658   $48.47   $48.45   $48.50  
  Purchase #5 $223.82   9.308%   $244.6532   $244.65   $244.65   $244.70  
  Purchase #6 $47.37   5.452%   $49.9526   $49.95   $49.95   $50.00  
  Purchase #7 $153.35   5.790%   $162.229   $162.23   $162.25   $162.20  
  7 purchase totals = $878.37       $957.3070   $957.31   $957.30   $957.40