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 $208.70   8.709%   $226.8757   $226.88   $226.90   $226.90  
  Purchase #2 $61.41   13.630%   $69.7802   $69.78   $69.80   $69.80  
  Purchase #3 $243.53   4.775%   $255.1586   $255.16   $255.15   $255.20  
  Purchase #4 $59.92   12.772%   $67.573   $67.57   $67.55   $67.60  
  Purchase #5 $230.63   6.118%   $244.7399   $244.74   $244.75   $244.70  
  Purchase #6 $212.61   10.695%   $235.3486   $235.35   $235.35   $235.30  
  Purchase #7 $135.58   3.484%   $140.3036   $140.30   $140.30   $140.30  
  7 purchase totals = $1,152.38       $1,239.7796   $1,239.78   $1,239.80   $1,239.80