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 $239.61   11.729%   $267.7139   $267.71   $267.70   $267.70  
  Purchase #2 $30.84   8.613%   $33.4962   $33.50   $33.50   $33.50  
  Purchase #3 $218.79   10.104%   $240.8965   $240.90   $240.90   $240.90  
  Purchase #4 $240.27   11.375%   $267.6007   $267.60   $267.60   $267.60  
  Purchase #5 $60.29   13.770%   $68.5919   $68.59   $68.60   $68.60  
  Purchase #6 $160.67   3.187%   $165.7906   $165.79   $165.80   $165.80  
  Purchase #7 $158.95   5.549%   $167.7701   $167.77   $167.75   $167.80  
  7 purchase totals = $1,109.42       $1,211.8599   $1,211.86   $1,211.85   $1,211.90