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 $30.71   5.550%   $32.4144   $32.41   $32.40   $32.40  
  Purchase #2 $238.96   6.559%   $254.6334   $254.63   $254.65   $254.60  
  Purchase #3 $212.67   4.371%   $221.9658   $221.97   $221.95   $222.00  
  Purchase #4 $241.96   8.635%   $262.8532   $262.85   $262.85   $262.90  
  Purchase #5 $205.72   9.218%   $224.6833   $224.68   $224.70   $224.70  
  Purchase #6 $11.89   11.834%   $13.2971   $13.30   $13.30   $13.30  
  Purchase #7 $46.75   13.263%   $52.9505   $52.95   $52.95   $53.00  
  7 purchase totals = $988.66       $1,062.7977   $1,062.79   $1,062.80   $1,062.90