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 $192.83   4.773%   $202.0338   $202.03   $202.05   $202.00  
  Purchase #2 $143.98   12.493%   $161.9674   $161.97   $161.95   $162.00  
  Purchase #3 $54.42   12.464%   $61.2029   $61.20   $61.20   $61.20  
  Purchase #4 $90.43   3.288%   $93.4033   $93.40   $93.40   $93.40  
  Purchase #5 $209.90   9.538%   $229.9203   $229.92   $229.90   $229.90  
  Purchase #6 $166.25   13.189%   $188.1767   $188.18   $188.20   $188.20  
  Purchase #7 $107.76   7.411%   $115.7461   $115.75   $115.75   $115.70  
  7 purchase totals = $965.57       $1,052.4505   $1,052.45   $1,052.45   $1,052.40