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 $92.73   11.635%   $103.5191   $103.52   $103.50   $103.50  
  Purchase #2 $138.98   9.786%   $152.5806   $152.58   $152.60   $152.60  
  Purchase #3 $41.32   5.223%   $43.4781   $43.48   $43.50   $43.50  
  Purchase #4 $71.80   4.323%   $74.9039   $74.90   $74.90   $74.90  
  Purchase #5 $110.27   10.667%   $122.0325   $122.03   $122.05   $122.00  
  Purchase #6 $114.41   9.221%   $124.9597   $124.96   $124.95   $125.00  
  Purchase #7 $124.53   8.806%   $135.4961   $135.50   $135.50   $135.50  
  7 purchase totals = $694.04       $756.9700   $756.97   $757.00   $757.00