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 $188.44   9.782%   $206.8732   $206.87   $206.85   $206.90  
  Purchase #2 $177.62   10.154%   $195.6555   $195.66   $195.65   $195.70  
  Purchase #3 $64.67   12.203%   $72.5617   $72.56   $72.55   $72.60  
  Purchase #4 $233.80   5.813%   $247.3908   $247.39   $247.40   $247.40  
  Purchase #5 $110.28   12.166%   $123.6967   $123.70   $123.70   $123.70  
  Purchase #6 $125.90   13.624%   $143.0526   $143.05   $143.05   $143.10  
  Purchase #7 $111.66   12.170%   $125.249   $125.25   $125.25   $125.20  
  7 purchase totals = $1,012.37       $1,114.4795   $1,114.48   $1,114.45   $1,114.60