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 $96.95   7.274%   $104.0021   $104.00   $104.00   $104.00  
  Purchase #2 $81.79   5.685%   $86.4398   $86.44   $86.45   $86.40  
  Purchase #3 $42.38   5.601%   $44.7537   $44.75   $44.75   $44.80  
  Purchase #4 $30.84   9.497%   $33.7689   $33.77   $33.75   $33.80  
  Purchase #5 $206.92   6.145%   $219.6352   $219.64   $219.65   $219.60  
  Purchase #6 $22.86   9.455%   $25.0214   $25.02   $25.00   $25.00  
  Purchase #7 $200.27   10.771%   $221.8411   $221.84   $221.85   $221.80  
  7 purchase totals = $682.01       $735.4622   $735.46   $735.45   $735.40