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 $77.34   8.652%   $84.0315   $84.03   $84.05   $84.00  
  Purchase #2 $167.55   7.627%   $180.329   $180.33   $180.35   $180.30  
  Purchase #3 $65.58   8.464%   $71.1307   $71.13   $71.15   $71.10  
  Purchase #4 $68.76   3.185%   $70.95   $70.95   $70.95   $71.00  
  Purchase #5 $30.72   12.222%   $34.4746   $34.47   $34.45   $34.50  
  Purchase #6 $178.81   8.589%   $194.168   $194.17   $194.15   $194.20  
  Purchase #7 $114.28   6.861%   $122.1208   $122.12   $122.10   $122.10  
  7 purchase totals = $703.04       $757.2046   $757.20   $757.20   $757.20