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 $89.56   5.812%   $94.7652   $94.77   $94.75   $94.80  
  Purchase #2 $146.70   10.159%   $161.6033   $161.60   $161.60   $161.60  
  Purchase #3 $250.41   12.237%   $281.0527   $281.05   $281.05   $281.10  
  Purchase #4 $227.82   8.200%   $246.5012   $246.50   $246.50   $246.50  
  Purchase #5 $221.63   11.608%   $247.3568   $247.36   $247.35   $247.40  
  Purchase #6 $176.29   6.120%   $187.0789   $187.08   $187.10   $187.10  
  Purchase #7 $102.86   10.188%   $113.3394   $113.34   $113.35   $113.30  
  7 purchase totals = $1,215.27       $1,331.6975   $1,331.70   $1,331.70   $1,331.80