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 $145.89   10.680%   $161.4711   $161.47   $161.45   $161.50  
  Purchase #2 $208.80   12.620%   $235.1506   $235.15   $235.15   $235.20  
  Purchase #3 $223.32   8.490%   $242.2799   $242.28   $242.30   $242.30  
  Purchase #4 $205.75   8.763%   $223.7799   $223.78   $223.80   $223.80  
  Purchase #5 $177.73   13.627%   $201.9493   $201.95   $201.95   $201.90  
  Purchase #6 $34.80   4.425%   $36.3399   $36.34   $36.35   $36.30  
  Purchase #7 $110.31   6.342%   $117.3059   $117.31   $117.30   $117.30  
  7 purchase totals = $1,106.60       $1,218.2766   $1,218.28   $1,218.30   $1,218.30