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 $222.33   8.603%   $241.457   $241.46   $241.45   $241.50  
  Purchase #2 $175.35   7.770%   $188.9747   $188.97   $188.95   $189.00  
  Purchase #3 $246.58   4.172%   $256.8673   $256.87   $256.85   $256.90  
  Purchase #4 $189.52   4.829%   $198.6719   $198.67   $198.65   $198.70  
  Purchase #5 $82.35   11.269%   $91.63   $91.63   $91.65   $91.60  
  Purchase #6 $221.29   12.567%   $249.0995   $249.10   $249.10   $249.10  
  Purchase #7 $176.65   13.349%   $200.231   $200.23   $200.25   $200.20  
  7 purchase totals = $1,314.07       $1,426.9314   $1,426.93   $1,426.90   $1,427.00