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 $118.75   6.684%   $126.6873   $126.69   $126.70   $126.70  
  Purchase #2 $129.38   6.754%   $138.1183   $138.12   $138.10   $138.10  
  Purchase #3 $82.91   13.862%   $94.403   $94.40   $94.40   $94.40  
  Purchase #4 $248.73   5.366%   $262.0769   $262.08   $262.10   $262.10  
  Purchase #5 $224.58   9.826%   $246.6472   $246.65   $246.65   $246.60  
  Purchase #6 $128.87   11.370%   $143.5225   $143.52   $143.50   $143.50  
  Purchase #7 $249.44   8.420%   $270.4428   $270.44   $270.45   $270.40  
  7 purchase totals = $1,182.66       $1,281.8980   $1,281.90   $1,281.90   $1,281.80