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 $217.94   11.432%   $242.8549   $242.85   $242.85   $242.90  
  Purchase #2 $176.52   11.163%   $196.2249   $196.22   $196.20   $196.20  
  Purchase #3 $16.69   5.873%   $17.6702   $17.67   $17.65   $17.70  
  Purchase #4 $203.99   10.264%   $224.9275   $224.93   $224.95   $224.90  
  Purchase #5 $149.80   9.726%   $164.3695   $164.37   $164.35   $164.40  
  Purchase #6 $92.50   4.381%   $96.5524   $96.55   $96.55   $96.60  
  Purchase #7 $96.50   13.352%   $109.3847   $109.38   $109.40   $109.40  
  7 purchase totals = $953.94       $1,051.9841   $1,051.97   $1,051.95   $1,052.10