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 $77.85   7.273%   $83.512   $83.51   $83.50   $83.50  
  Purchase #2 $247.62   5.866%   $262.1454   $262.15   $262.15   $262.10  
  Purchase #3 $176.48   10.376%   $194.7916   $194.79   $194.80   $194.80  
  Purchase #4 $139.89   7.780%   $150.7734   $150.77   $150.75   $150.80  
  Purchase #5 $107.41   11.353%   $119.6043   $119.60   $119.60   $119.60  
  Purchase #6 $137.95   11.601%   $153.9536   $153.95   $153.95   $154.00  
  Purchase #7 $74.42   8.665%   $80.8685   $80.87   $80.85   $80.90  
  7 purchase totals = $961.62       $1,045.6488   $1,045.64   $1,045.60   $1,045.70