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 $119.99   13.764%   $136.5054   $136.51   $136.50   $136.50  
  Purchase #2 $113.68   3.250%   $117.3746   $117.37   $117.35   $117.40  
  Purchase #3 $144.96   10.576%   $160.291   $160.29   $160.30   $160.30  
  Purchase #4 $233.96   13.624%   $265.8347   $265.83   $265.85   $265.80  
  Purchase #5 $218.31   10.322%   $240.844   $240.84   $240.85   $240.80  
  Purchase #6 $41.87   6.631%   $44.6464   $44.65   $44.65   $44.60  
  Purchase #7 $94.86   9.677%   $104.0396   $104.04   $104.05   $104.00  
  7 purchase totals = $967.63       $1,069.5357   $1,069.53   $1,069.55   $1,069.40