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 $227.94   6.161%   $241.9834   $241.98   $242.00   $242.00  
  Purchase #2 $238.67   7.772%   $257.2194   $257.22   $257.20   $257.20  
  Purchase #3 $124.87   4.873%   $130.9549   $130.95   $130.95   $131.00  
  Purchase #4 $154.45   11.751%   $172.5994   $172.60   $172.60   $172.60  
  Purchase #5 $156.78   6.150%   $166.422   $166.42   $166.40   $166.40  
  Purchase #6 $222.79   8.872%   $242.5559   $242.56   $242.55   $242.60  
  Purchase #7 $244.30   13.776%   $277.9548   $277.95   $277.95   $278.00  
  7 purchase totals = $1,369.80       $1,489.6898   $1,489.68   $1,489.65   $1,489.80