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 $60.86   8.215%   $65.8596   $65.86   $65.85   $65.90  
  Purchase #2 $129.73   13.634%   $147.4174   $147.42   $147.40   $147.40  
  Purchase #3 $156.85   10.189%   $172.8314   $172.83   $172.85   $172.80  
  Purchase #4 $244.59   3.438%   $252.999   $253.00   $253.00   $253.00  
  Purchase #5 $189.88   7.549%   $204.214   $204.21   $204.20   $204.20  
  Purchase #6 $239.77   10.813%   $265.6963   $265.70   $265.70   $265.70  
  Purchase #7 $194.41   11.478%   $216.7244   $216.72   $216.70   $216.70  
  7 purchase totals = $1,216.09       $1,325.7421   $1,325.74   $1,325.70   $1,325.70