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 $146.93   10.775%   $162.7617   $162.76   $162.75   $162.80  
  Purchase #2 $242.60   4.565%   $253.6747   $253.67   $253.65   $253.70  
  Purchase #3 $118.48   8.686%   $128.7712   $128.77   $128.75   $128.80  
  Purchase #4 $230.46   7.540%   $247.8367   $247.84   $247.85   $247.80  
  Purchase #5 $200.85   4.463%   $209.8139   $209.81   $209.80   $209.80  
  Purchase #6 $53.97   6.527%   $57.4926   $57.49   $57.50   $57.50  
  Purchase #7 $163.95   7.532%   $176.2987   $176.30   $176.30   $176.30  
  7 purchase totals = $1,157.24       $1,236.6495   $1,236.64   $1,236.60   $1,236.70