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 $244.61   9.164%   $267.0261   $267.03   $267.05   $267.00  
  Purchase #2 $58.31   8.405%   $63.211   $63.21   $63.20   $63.20  
  Purchase #3 $90.29   13.517%   $102.4945   $102.49   $102.50   $102.50  
  Purchase #4 $25.76   11.541%   $28.733   $28.73   $28.75   $28.70  
  Purchase #5 $98.76   10.486%   $109.116   $109.12   $109.10   $109.10  
  Purchase #6 $208.57   3.295%   $215.4424   $215.44   $215.45   $215.40  
  Purchase #7 $221.58   13.693%   $251.9209   $251.92   $251.90   $251.90  
  7 purchase totals = $947.88       $1,037.9439   $1,037.94   $1,037.95   $1,037.80