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 $111.40   11.743%   $124.4817   $124.48   $124.50   $124.50  
  Purchase #2 $186.96   9.311%   $204.3678   $204.37   $204.35   $204.40  
  Purchase #3 $168.45   7.270%   $180.6963   $180.70   $180.70   $180.70  
  Purchase #4 $243.87   7.451%   $262.0408   $262.04   $262.05   $262.00  
  Purchase #5 $231.36   13.549%   $262.707   $262.71   $262.70   $262.70  
  Purchase #6 $148.25   3.672%   $153.6937   $153.69   $153.70   $153.70  
  Purchase #7 $102.80   3.439%   $106.3353   $106.34   $106.35   $106.30  
  7 purchase totals = $1,193.09       $1,294.3226   $1,294.33   $1,294.35   $1,294.30