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 $219.81   11.734%   $245.6025   $245.60   $245.60   $245.60  
  Purchase #2 $103.87   12.624%   $116.9825   $116.98   $117.00   $117.00  
  Purchase #3 $41.59   13.688%   $47.2828   $47.28   $47.30   $47.30  
  Purchase #4 $231.69   8.853%   $252.2015   $252.20   $252.20   $252.20  
  Purchase #5 $95.31   9.245%   $104.1214   $104.12   $104.10   $104.10  
  Purchase #6 $167.33   11.614%   $186.7637   $186.76   $186.75   $186.80  
  Purchase #7 $35.74   10.729%   $39.5745   $39.57   $39.55   $39.60  
  7 purchase totals = $895.34       $992.5289   $992.51   $992.50   $992.60