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 $38.79   13.621%   $44.0736   $44.07   $44.05   $44.10  
  Purchase #2 $154.29   10.785%   $170.9302   $170.93   $170.95   $170.90  
  Purchase #3 $240.84   4.244%   $251.0612   $251.06   $251.05   $251.10  
  Purchase #4 $220.37   10.677%   $243.8989   $243.90   $243.90   $243.90  
  Purchase #5 $96.53   7.357%   $103.6317   $103.63   $103.65   $103.60  
  Purchase #6 $206.45   3.558%   $213.7955   $213.80   $213.80   $213.80  
  Purchase #7 $59.97   10.391%   $66.2015   $66.20   $66.20   $66.20  
  7 purchase totals = $1,017.24       $1,093.5926   $1,093.59   $1,093.60   $1,093.60