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 $134.25   13.761%   $152.7241   $152.72   $152.70   $152.70  
  Purchase #2 $152.98   7.402%   $164.3036   $164.30   $164.30   $164.30  
  Purchase #3 $245.35   10.770%   $271.7742   $271.77   $271.75   $271.80  
  Purchase #4 $34.81   4.129%   $36.2473   $36.25   $36.25   $36.20  
  Purchase #5 $106.78   6.359%   $113.5701   $113.57   $113.55   $113.60  
  Purchase #6 $33.33   4.383%   $34.7909   $34.79   $34.80   $34.80  
  Purchase #7 $250.75   6.147%   $266.1636   $266.16   $266.15   $266.20  
  7 purchase totals = $958.25       $1,039.5738   $1,039.56   $1,039.50   $1,039.60