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 $214.78   11.674%   $239.8534   $239.85   $239.85   $239.90  
  Purchase #2 $153.94   6.632%   $164.1493   $164.15   $164.15   $164.10  
  Purchase #3 $193.37   13.361%   $219.2062   $219.21   $219.20   $219.20  
  Purchase #4 $92.85   6.581%   $98.9605   $98.96   $98.95   $99.00  
  Purchase #5 $203.85   7.498%   $219.1347   $219.13   $219.15   $219.10  
  Purchase #6 $230.80   5.621%   $243.7733   $243.77   $243.75   $243.80  
  Purchase #7 $60.81   8.178%   $65.783   $65.78   $65.80   $65.80  
  7 purchase totals = $1,150.40       $1,250.8604   $1,250.85   $1,250.85   $1,250.90