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 $245.93   10.432%   $271.5854   $271.59   $271.60   $271.60  
  Purchase #2 $175.28   9.441%   $191.8282   $191.83   $191.85   $191.80  
  Purchase #3 $170.32   7.132%   $182.4672   $182.47   $182.45   $182.50  
  Purchase #4 $98.35   3.529%   $101.8208   $101.82   $101.80   $101.80  
  Purchase #5 $183.65   12.239%   $206.1269   $206.13   $206.15   $206.10  
  Purchase #6 $68.44   12.871%   $77.2489   $77.25   $77.25   $77.20  
  Purchase #7 $153.84   11.739%   $171.8993   $171.90   $171.90   $171.90  
  7 purchase totals = $1,095.81       $1,202.9767   $1,202.99   $1,203.00   $1,202.90