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 $68.85   7.144%   $73.7686   $73.77   $73.75   $73.80  
  Purchase #2 $81.71   5.449%   $86.1624   $86.16   $86.15   $86.20  
  Purchase #3 $80.31   11.430%   $89.4894   $89.49   $89.50   $89.50  
  Purchase #4 $157.73   7.281%   $169.2143   $169.21   $169.20   $169.20  
  Purchase #5 $68.50   10.862%   $75.9405   $75.94   $75.95   $75.90  
  Purchase #6 $153.65   7.557%   $165.2613   $165.26   $165.25   $165.30  
  Purchase #7 $90.89   11.386%   $101.2387   $101.24   $101.25   $101.20  
  7 purchase totals = $701.64       $761.0752   $761.07   $761.05   $761.10