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 $218.62   12.189%   $245.2676   $245.27   $245.25   $245.30  
  Purchase #2 $131.87   11.819%   $147.4557   $147.46   $147.45   $147.50  
  Purchase #3 $60.53   7.413%   $65.0171   $65.02   $65.00   $65.00  
  Purchase #4 $227.95   12.703%   $256.9065   $256.91   $256.90   $256.90  
  Purchase #5 $183.86   11.839%   $205.6272   $205.63   $205.65   $205.60  
  Purchase #6 $85.54   11.431%   $95.3181   $95.32   $95.30   $95.30  
  Purchase #7 $192.91   5.736%   $203.9753   $203.98   $204.00   $204.00  
  7 purchase totals = $1,101.28       $1,219.5675   $1,219.59   $1,219.55   $1,219.60