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 $124.99   13.249%   $141.5499   $141.55   $141.55   $141.50  
  Purchase #2 $112.84   12.514%   $126.9608   $126.96   $126.95   $127.00  
  Purchase #3 $110.90   6.379%   $117.9743   $117.97   $117.95   $118.00  
  Purchase #4 $51.31   4.353%   $53.5435   $53.54   $53.55   $53.50  
  Purchase #5 $40.52   5.118%   $42.5938   $42.59   $42.60   $42.60  
  Purchase #6 $63.46   8.128%   $68.618   $68.62   $68.60   $68.60  
  Purchase #7 $75.37   7.466%   $80.9971   $81.00   $81.00   $81.00  
  7 purchase totals = $579.39       $632.2374   $632.23   $632.20   $632.20