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 $172.85   5.493%   $182.3447   $182.34   $182.35   $182.30  
  Purchase #2 $32.57   8.556%   $35.3567   $35.36   $35.35   $35.40  
  Purchase #3 $157.28   4.485%   $164.334   $164.33   $164.35   $164.30  
  Purchase #4 $120.58   4.492%   $125.9965   $126.00   $126.00   $126.00  
  Purchase #5 $213.74   4.407%   $223.1595   $223.16   $223.15   $223.20  
  Purchase #6 $198.36   6.595%   $211.4418   $211.44   $211.45   $211.40  
  Purchase #7 $128.25   9.442%   $140.3594   $140.36   $140.35   $140.40  
  7 purchase totals = $1,023.63       $1,082.9926   $1,082.99   $1,083.00   $1,083.00