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 $219.85   10.626%   $243.2113   $243.21   $243.20   $243.20  
  Purchase #2 $94.77   9.687%   $103.9504   $103.95   $103.95   $104.00  
  Purchase #3 $87.81   8.858%   $95.5882   $95.59   $95.60   $95.60  
  Purchase #4 $82.85   4.268%   $86.386   $86.39   $86.40   $86.40  
  Purchase #5 $195.80   6.532%   $208.5897   $208.59   $208.60   $208.60  
  Purchase #6 $27.99   12.303%   $31.4336   $31.43   $31.45   $31.40  
  Purchase #7 $109.95   8.785%   $119.6091   $119.61   $119.60   $119.60  
  7 purchase totals = $819.02       $888.7683   $888.77   $888.80   $888.80