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 $182.42   12.542%   $205.2991   $205.30   $205.30   $205.30  
  Purchase #2 $219.43   9.730%   $240.7805   $240.78   $240.80   $240.80  
  Purchase #3 $67.26   5.564%   $71.0023   $71.00   $71.00   $71.00  
  Purchase #4 $139.93   7.779%   $150.8152   $150.82   $150.80   $150.80  
  Purchase #5 $195.73   13.420%   $221.997   $222.00   $222.00   $222.00  
  Purchase #6 $234.66   11.677%   $262.0612   $262.06   $262.05   $262.10  
  Purchase #7 $130.72   9.834%   $143.575   $143.58   $143.60   $143.60  
  7 purchase totals = $1,170.15       $1,295.5303   $1,295.54   $1,295.55   $1,295.60