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 $111.85   12.692%   $126.046   $126.05   $126.05   $126.00  
  Purchase #2 $155.83   10.166%   $171.6717   $171.67   $171.65   $171.70  
  Purchase #3 $181.54   9.258%   $198.347   $198.35   $198.35   $198.30  
  Purchase #4 $120.97   10.248%   $133.367   $133.37   $133.35   $133.40  
  Purchase #5 $41.93   13.224%   $47.4748   $47.47   $47.45   $47.50  
  Purchase #6 $49.47   8.416%   $53.6334   $53.63   $53.65   $53.60  
  Purchase #7 $244.80   10.778%   $271.1845   $271.18   $271.20   $271.20  
  7 purchase totals = $906.39       $1,001.7244   $1,001.72   $1,001.70   $1,001.70