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 $243.25   7.689%   $261.9535   $261.95   $261.95   $262.00  
  Purchase #2 $110.55   8.811%   $120.2906   $120.29   $120.30   $120.30  
  Purchase #3 $216.50   13.475%   $245.6734   $245.67   $245.65   $245.70  
  Purchase #4 $104.97   12.764%   $118.3684   $118.37   $118.35   $118.40  
  Purchase #5 $163.44   5.493%   $172.4178   $172.42   $172.40   $172.40  
  Purchase #6 $189.50   8.120%   $204.8874   $204.89   $204.90   $204.90  
  Purchase #7 $142.85   7.631%   $153.7509   $153.75   $153.75   $153.80  
  7 purchase totals = $1,171.06       $1,277.3420   $1,277.34   $1,277.30   $1,277.50