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 $228.67   8.165%   $247.3409   $247.34   $247.35   $247.30  
  Purchase #2 $93.83   11.146%   $104.2883   $104.29   $104.30   $104.30  
  Purchase #3 $212.84   3.867%   $221.0705   $221.07   $221.05   $221.10  
  Purchase #4 $220.38   3.302%   $227.6569   $227.66   $227.65   $227.70  
  Purchase #5 $203.60   13.862%   $231.823   $231.82   $231.80   $231.80  
  Purchase #6 $185.31   11.481%   $206.5854   $206.59   $206.60   $206.60  
  Purchase #7 $25.90   6.671%   $27.6278   $27.63   $27.65   $27.60  
  7 purchase totals = $1,170.53       $1,266.3928   $1,266.40   $1,266.40   $1,266.40