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 $234.73   8.291%   $254.1915   $254.19   $254.20   $254.20  
  Purchase #2 $139.58   7.728%   $150.3667   $150.37   $150.35   $150.40  
  Purchase #3 $240.61   11.339%   $267.8928   $267.89   $267.90   $267.90  
  Purchase #4 $163.49   5.697%   $172.804   $172.80   $172.80   $172.80  
  Purchase #5 $25.56   4.337%   $26.6685   $26.67   $26.65   $26.70  
  Purchase #6 $57.25   5.766%   $60.551   $60.55   $60.55   $60.60  
  Purchase #7 $14.50   11.241%   $16.1299   $16.13   $16.15   $16.10  
  7 purchase totals = $875.72       $948.6044   $948.60   $948.60   $948.70