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 $228.89   13.482%   $259.7489   $259.75   $259.75   $259.70  
  Purchase #2 $190.33   7.233%   $204.0966   $204.10   $204.10   $204.10  
  Purchase #3 $114.56   5.417%   $120.7657   $120.77   $120.75   $120.80  
  Purchase #4 $22.94   3.265%   $23.689   $23.69   $23.70   $23.70  
  Purchase #5 $177.45   10.412%   $195.9261   $195.93   $195.95   $195.90  
  Purchase #6 $195.87   5.751%   $207.1345   $207.13   $207.15   $207.10  
  Purchase #7 $178.60   12.788%   $201.4394   $201.44   $201.45   $201.40  
  7 purchase totals = $1,108.64       $1,212.8002   $1,212.81   $1,212.85   $1,212.70