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 $228.69   12.680%   $257.6879   $257.69   $257.70   $257.70  
  Purchase #2 $172.29   3.833%   $178.8939   $178.89   $178.90   $178.90  
  Purchase #3 $220.90   11.802%   $246.9706   $246.97   $246.95   $247.00  
  Purchase #4 $101.59   4.790%   $106.4562   $106.46   $106.45   $106.50  
  Purchase #5 $84.56   8.873%   $92.063   $92.06   $92.05   $92.10  
  Purchase #6 $72.99   4.291%   $76.122   $76.12   $76.10   $76.10  
  Purchase #7 $53.46   8.820%   $58.1752   $58.18   $58.20   $58.20  
  7 purchase totals = $934.48       $1,016.3688   $1,016.37   $1,016.35   $1,016.50