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 $92.89   5.713%   $98.1968   $98.20   $98.20   $98.20  
  Purchase #2 $181.61   12.566%   $204.4311   $204.43   $204.45   $204.40  
  Purchase #3 $182.36   3.358%   $188.4836   $188.48   $188.50   $188.50  
  Purchase #4 $235.42   8.458%   $255.3318   $255.33   $255.35   $255.30  
  Purchase #5 $18.66   10.327%   $20.587   $20.59   $20.60   $20.60  
  Purchase #6 $242.28   12.217%   $271.8793   $271.88   $271.90   $271.90  
  Purchase #7 $243.43   8.537%   $264.2116   $264.21   $264.20   $264.20  
  7 purchase totals = $1,196.65       $1,303.1212   $1,303.12   $1,303.20   $1,303.10