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 $53.98   8.622%   $58.6342   $58.63   $58.65   $58.60  
  Purchase #2 $191.40   8.312%   $207.3092   $207.31   $207.30   $207.30  
  Purchase #3 $157.71   6.218%   $167.5164   $167.52   $167.50   $167.50  
  Purchase #4 $123.72   11.327%   $137.7338   $137.73   $137.75   $137.70  
  Purchase #5 $190.64   8.588%   $207.0122   $207.01   $207.00   $207.00  
  Purchase #6 $121.77   13.316%   $137.9849   $137.98   $138.00   $138.00  
  Purchase #7 $137.87   13.475%   $156.448   $156.45   $156.45   $156.40  
  7 purchase totals = $977.09       $1,072.6387   $1,072.63   $1,072.65   $1,072.50