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 $112.25   10.531%   $124.071   $124.07   $124.05   $124.10  
  Purchase #2 $16.80   4.121%   $17.4923   $17.49   $17.50   $17.50  
  Purchase #3 $76.80   3.830%   $79.7414   $79.74   $79.75   $79.70  
  Purchase #4 $211.92   3.657%   $219.6699   $219.67   $219.65   $219.70  
  Purchase #5 $239.99   4.384%   $250.5112   $250.51   $250.50   $250.50  
  Purchase #6 $153.31   10.786%   $169.846   $169.85   $169.85   $169.80  
  Purchase #7 $85.72   6.792%   $91.5421   $91.54   $91.55   $91.50  
  7 purchase totals = $896.79       $952.8739   $952.87   $952.85   $952.80