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 $203.52   9.477%   $222.8076   $222.81   $222.80   $222.80  
  Purchase #2 $215.91   6.687%   $230.3479   $230.35   $230.35   $230.30  
  Purchase #3 $161.47   6.286%   $171.62   $171.62   $171.60   $171.60  
  Purchase #4 $22.37   6.744%   $23.8786   $23.88   $23.90   $23.90  
  Purchase #5 $222.89   12.153%   $249.9778   $249.98   $250.00   $250.00  
  Purchase #6 $5.50   5.159%   $5.7837   $5.78   $5.80   $5.80  
  Purchase #7 $54.32   7.796%   $58.5548   $58.55   $58.55   $58.60  
  7 purchase totals = $885.98       $962.9704   $962.97   $963.00   $963.00