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 $183.43   12.826%   $206.9567   $206.96   $206.95   $207.00  
  Purchase #2 $80.46   12.805%   $90.7629   $90.76   $90.75   $90.80  
  Purchase #3 $40.86   11.150%   $45.4159   $45.42   $45.40   $45.40  
  Purchase #4 $45.68   8.695%   $49.6519   $49.65   $49.65   $49.70  
  Purchase #5 $93.53   10.577%   $103.4227   $103.42   $103.40   $103.40  
  Purchase #6 $237.72   4.442%   $248.2795   $248.28   $248.30   $248.30  
  Purchase #7 $79.75   11.507%   $88.9268   $88.93   $88.95   $88.90  
  7 purchase totals = $761.43       $833.4164   $833.42   $833.40   $833.50