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 $243.53   3.322%   $251.6201   $251.62   $251.60   $251.60  
  Purchase #2 $66.83   10.211%   $73.654   $73.65   $73.65   $73.70  
  Purchase #3 $70.38   4.771%   $73.7378   $73.74   $73.75   $73.70  
  Purchase #4 $239.38   5.248%   $251.9427   $251.94   $251.95   $251.90  
  Purchase #5 $95.60   10.182%   $105.334   $105.33   $105.35   $105.30  
  Purchase #6 $107.68   10.609%   $119.1038   $119.10   $119.10   $119.10  
  Purchase #7 $154.80   4.666%   $162.023   $162.02   $162.00   $162.00  
  7 purchase totals = $978.20       $1,037.4154   $1,037.40   $1,037.40   $1,037.30