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 $181.38   13.837%   $206.4776   $206.48   $206.50   $206.50  
  Purchase #2 $20.60   13.176%   $23.3143   $23.31   $23.30   $23.30  
  Purchase #3 $214.63   9.129%   $234.2236   $234.22   $234.20   $234.20  
  Purchase #4 $21.59   11.263%   $24.0217   $24.02   $24.00   $24.00  
  Purchase #5 $150.75   13.273%   $170.759   $170.76   $170.75   $170.80  
  Purchase #6 $222.58   11.801%   $248.8467   $248.85   $248.85   $248.80  
  Purchase #7 $92.40   13.421%   $104.801   $104.80   $104.80   $104.80  
  7 purchase totals = $903.93       $1,012.4439   $1,012.44   $1,012.40   $1,012.40