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 $220.82   7.177%   $236.6683   $236.67   $236.65   $236.70  
  Purchase #2 $90.44   5.532%   $95.4431   $95.44   $95.45   $95.40  
  Purchase #3 $41.86   6.403%   $44.5403   $44.54   $44.55   $44.50  
  Purchase #4 $205.66   5.484%   $216.9384   $216.94   $216.95   $216.90  
  Purchase #5 $174.26   6.270%   $185.1861   $185.19   $185.20   $185.20  
  Purchase #6 $235.30   11.858%   $263.2019   $263.20   $263.20   $263.20  
  Purchase #7 $17.36   5.851%   $18.3757   $18.38   $18.40   $18.40  
  7 purchase totals = $985.70       $1,060.3538   $1,060.36   $1,060.40   $1,060.30