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 $85.72   7.281%   $91.9613   $91.96   $91.95   $92.00  
  Purchase #2 $24.61   6.140%   $26.1211   $26.12   $26.10   $26.10  
  Purchase #3 $36.39   7.456%   $39.1032   $39.10   $39.10   $39.10  
  Purchase #4 $244.40   6.348%   $259.9145   $259.91   $259.90   $259.90  
  Purchase #5 $23.46   11.494%   $26.1565   $26.16   $26.15   $26.20  
  Purchase #6 $83.32   12.575%   $93.7975   $93.80   $93.80   $93.80  
  Purchase #7 $24.42   9.399%   $26.7152   $26.72   $26.70   $26.70  
  7 purchase totals = $522.32       $563.7693   $563.77   $563.70   $563.80