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 $91.41   4.853%   $95.8461   $95.85   $95.85   $95.80  
  Purchase #2 $24.97   3.573%   $25.8622   $25.86   $25.85   $25.90  
  Purchase #3 $12.70   5.577%   $13.4083   $13.41   $13.40   $13.40  
  Purchase #4 $203.47   13.866%   $231.6832   $231.68   $231.70   $231.70  
  Purchase #5 $231.70   8.598%   $251.6216   $251.62   $251.60   $251.60  
  Purchase #6 $219.71   11.658%   $245.3238   $245.32   $245.30   $245.30  
  Purchase #7 $136.67   3.203%   $141.0475   $141.05   $141.05   $141.00  
  7 purchase totals = $920.63       $1,004.7927   $1,004.79   $1,004.75   $1,004.70