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 $242.96   7.538%   $261.2743   $261.27   $261.25   $261.30  
  Purchase #2 $219.68   6.840%   $234.7061   $234.71   $234.70   $234.70  
  Purchase #3 $10.99   6.268%   $11.6789   $11.68   $11.70   $11.70  
  Purchase #4 $250.29   6.446%   $266.4237   $266.42   $266.40   $266.40  
  Purchase #5 $29.71   11.792%   $33.2134   $33.21   $33.20   $33.20  
  Purchase #6 $202.66   7.831%   $218.5303   $218.53   $218.55   $218.50  
  Purchase #7 $203.42   3.195%   $209.9193   $209.92   $209.90   $209.90  
  7 purchase totals = $1,159.71       $1,235.7460   $1,235.74   $1,235.70   $1,235.70