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 $244.98   9.388%   $267.9787   $267.98   $268.00   $268.00  
  Purchase #2 $217.43   8.610%   $236.1507   $236.15   $236.15   $236.20  
  Purchase #3 $47.52   13.591%   $53.9784   $53.98   $54.00   $54.00  
  Purchase #4 $191.38   12.502%   $215.3063   $215.31   $215.30   $215.30  
  Purchase #5 $212.57   7.418%   $228.3384   $228.34   $228.35   $228.30  
  Purchase #6 $60.83   11.627%   $67.9027   $67.90   $67.90   $67.90  
  Purchase #7 $212.98   11.575%   $237.6324   $237.63   $237.65   $237.60  
  7 purchase totals = $1,187.69       $1,307.2876   $1,307.29   $1,307.35   $1,307.30