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 $49.28   13.339%   $55.8535   $55.85   $55.85   $55.90  
  Purchase #2 $202.47   8.440%   $219.5585   $219.56   $219.55   $219.60  
  Purchase #3 $67.58   7.470%   $72.6282   $72.63   $72.65   $72.60  
  Purchase #4 $90.61   7.357%   $97.2762   $97.28   $97.30   $97.30  
  Purchase #5 $95.83   9.574%   $105.0048   $105.00   $105.00   $105.00  
  Purchase #6 $177.65   9.190%   $193.976   $193.98   $194.00   $194.00  
  Purchase #7 $85.58   4.379%   $89.3275   $89.33   $89.35   $89.30  
  7 purchase totals = $769.00       $833.6247   $833.63   $833.70   $833.70