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 $119.33   10.277%   $131.5935   $131.59   $131.60   $131.60  
  Purchase #2 $229.70   12.339%   $258.0427   $258.04   $258.05   $258.00  
  Purchase #3 $138.57   10.118%   $152.5905   $152.59   $152.60   $152.60  
  Purchase #4 $30.61   13.669%   $34.7941   $34.79   $34.80   $34.80  
  Purchase #5 $7.96   6.361%   $8.4663   $8.47   $8.45   $8.50  
  Purchase #6 $90.35   12.485%   $101.6302   $101.63   $101.65   $101.60  
  Purchase #7 $65.84   9.250%   $71.9302   $71.93   $71.95   $71.90  
  7 purchase totals = $682.36       $759.0475   $759.04   $759.10   $759.00