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 $196.85   3.414%   $203.5705   $203.57   $203.55   $203.60  
  Purchase #2 $179.26   8.508%   $194.5114   $194.51   $194.50   $194.50  
  Purchase #3 $219.99   4.127%   $229.069   $229.07   $229.05   $229.10  
  Purchase #4 $28.40   10.484%   $31.3775   $31.38   $31.40   $31.40  
  Purchase #5 $132.67   6.672%   $141.5217   $141.52   $141.50   $141.50  
  Purchase #6 $173.63   13.659%   $197.3461   $197.35   $197.35   $197.30  
  Purchase #7 $30.48   5.543%   $32.1695   $32.17   $32.15   $32.20  
  7 purchase totals = $961.28       $1,029.5657   $1,029.57   $1,029.50   $1,029.60