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 $56.54   9.747%   $62.051   $62.05   $62.05   $62.10  
  Purchase #2 $8.38   7.417%   $9.0015   $9.00   $9.00   $9.00  
  Purchase #3 $232.71   9.410%   $254.608   $254.61   $254.60   $254.60  
  Purchase #4 $87.91   12.371%   $98.7853   $98.79   $98.80   $98.80  
  Purchase #5 $31.95   13.597%   $36.2942   $36.29   $36.30   $36.30  
  Purchase #6 $94.71   8.491%   $102.7518   $102.75   $102.75   $102.80  
  Purchase #7 $81.39   9.868%   $89.4216   $89.42   $89.40   $89.40  
  7 purchase totals = $593.59       $652.9134   $652.91   $652.90   $653.00