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 $88.62   4.219%   $92.3589   $92.36   $92.35   $92.40  
  Purchase #2 $13.44   7.713%   $14.4766   $14.48   $14.50   $14.50  
  Purchase #3 $157.34   4.471%   $164.3747   $164.37   $164.35   $164.40  
  Purchase #4 $87.91   8.749%   $95.6012   $95.60   $95.60   $95.60  
  Purchase #5 $35.80   11.533%   $39.9288   $39.93   $39.95   $39.90  
  Purchase #6 $146.96   4.807%   $154.0244   $154.02   $154.00   $154.00  
  Purchase #7 $142.67   9.581%   $156.3392   $156.34   $156.35   $156.30  
  7 purchase totals = $672.74       $717.1038   $717.10   $717.10   $717.10