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 $114.74   9.154%   $125.2433   $125.24   $125.25   $125.20  
  Purchase #2 $19.58   9.231%   $21.3874   $21.39   $21.40   $21.40  
  Purchase #3 $185.84   5.501%   $196.0631   $196.06   $196.05   $196.10  
  Purchase #4 $41.47   9.347%   $45.3462   $45.35   $45.35   $45.30  
  Purchase #5 $124.55   7.319%   $133.6658   $133.67   $133.65   $133.70  
  Purchase #6 $55.66   4.847%   $58.3578   $58.36   $58.35   $58.40  
  Purchase #7 $66.77   12.171%   $74.8966   $74.90   $74.90   $74.90  
  7 purchase totals = $608.61       $654.9602   $654.97   $654.95   $655.00