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 $91.93   3.575%   $95.2165   $95.22   $95.20   $95.20  
  Purchase #2 $120.52   12.519%   $135.6079   $135.61   $135.60   $135.60  
  Purchase #3 $66.93   3.563%   $69.3147   $69.31   $69.30   $69.30  
  Purchase #4 $116.47   6.275%   $123.7785   $123.78   $123.80   $123.80  
  Purchase #5 $245.96   4.716%   $257.5595   $257.56   $257.55   $257.60  
  Purchase #6 $10.99   4.649%   $11.5009   $11.50   $11.50   $11.50  
  Purchase #7 $247.88   3.663%   $256.9598   $256.96   $256.95   $257.00  
  7 purchase totals = $900.68       $949.9378   $949.94   $949.90   $950.00