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 $196.52   3.602%   $203.5987   $203.60   $203.60   $203.60  
  Purchase #2 $144.55   11.131%   $160.6399   $160.64   $160.65   $160.60  
  Purchase #3 $177.28   6.270%   $188.3955   $188.40   $188.40   $188.40  
  Purchase #4 $16.37   3.465%   $16.9372   $16.94   $16.95   $16.90  
  Purchase #5 $102.76   10.849%   $113.9084   $113.91   $113.90   $113.90  
  Purchase #6 $126.53   13.182%   $143.2092   $143.21   $143.20   $143.20  
  Purchase #7 $174.89   13.176%   $197.9335   $197.93   $197.95   $197.90  
  7 purchase totals = $938.90       $1,024.6224   $1,024.63   $1,024.65   $1,024.50