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 $104.67   12.813%   $118.0814   $118.08   $118.10   $118.10  
  Purchase #2 $162.43   12.171%   $182.1994   $182.20   $182.20   $182.20  
  Purchase #3 $243.47   13.692%   $276.8059   $276.81   $276.80   $276.80  
  Purchase #4 $203.33   10.466%   $224.6105   $224.61   $224.60   $224.60  
  Purchase #5 $14.39   6.778%   $15.3654   $15.37   $15.35   $15.40  
  Purchase #6 $105.95   7.576%   $113.9768   $113.98   $114.00   $114.00  
  Purchase #7 $110.65   12.293%   $124.2522   $124.25   $124.25   $124.30  
  7 purchase totals = $944.89       $1,055.2916   $1,055.30   $1,055.30   $1,055.40