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 $33.65   7.556%   $36.1926   $36.19   $36.20   $36.20  
  Purchase #2 $56.91   4.741%   $59.6081   $59.61   $59.60   $59.60  
  Purchase #3 $167.55   5.572%   $176.8859   $176.89   $176.90   $176.90  
  Purchase #4 $222.76   9.444%   $243.7975   $243.80   $243.80   $243.80  
  Purchase #5 $76.45   9.871%   $83.9964   $84.00   $84.00   $84.00  
  Purchase #6 $79.75   10.697%   $88.2809   $88.28   $88.30   $88.30  
  Purchase #7 $19.86   5.342%   $20.9209   $20.92   $20.90   $20.90  
  7 purchase totals = $656.93       $709.6823   $709.69   $709.70   $709.70