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 $216.58   11.637%   $241.7834   $241.78   $241.80   $241.80  
  Purchase #2 $208.57   12.843%   $235.3566   $235.36   $235.35   $235.40  
  Purchase #3 $77.32   9.812%   $84.9066   $84.91   $84.90   $84.90  
  Purchase #4 $166.37   12.823%   $187.7036   $187.70   $187.70   $187.70  
  Purchase #5 $76.91   9.164%   $83.958   $83.96   $83.95   $84.00  
  Purchase #6 $239.35   9.272%   $261.5425   $261.54   $261.55   $261.50  
  Purchase #7 $237.51   3.859%   $246.6755   $246.68   $246.70   $246.70  
  7 purchase totals = $1,222.61       $1,341.9262   $1,341.93   $1,341.95   $1,342.00