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 $208.34   8.309%   $225.651   $225.65   $225.65   $225.70  
  Purchase #2 $189.40   3.293%   $195.6369   $195.64   $195.65   $195.60  
  Purchase #3 $156.26   4.125%   $162.7057   $162.71   $162.70   $162.70  
  Purchase #4 $26.67   5.731%   $28.1985   $28.20   $28.20   $28.20  
  Purchase #5 $46.92   12.802%   $52.9267   $52.93   $52.95   $52.90  
  Purchase #6 $74.49   4.220%   $77.6335   $77.63   $77.65   $77.60  
  Purchase #7 $75.55   13.135%   $85.4735   $85.47   $85.45   $85.50  
  7 purchase totals = $777.63       $828.2258   $828.23   $828.25   $828.20