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 $247.36   6.248%   $262.8151   $262.82   $262.80   $262.80  
  Purchase #2 $148.94   4.500%   $155.6423   $155.64   $155.65   $155.60  
  Purchase #3 $173.49   11.222%   $192.959   $192.96   $192.95   $193.00  
  Purchase #4 $68.25   10.865%   $75.6654   $75.67   $75.65   $75.70  
  Purchase #5 $165.61   4.577%   $173.19   $173.19   $173.20   $173.20  
  Purchase #6 $212.40   10.316%   $234.3112   $234.31   $234.30   $234.30  
  Purchase #7 $124.77   9.513%   $136.6394   $136.64   $136.65   $136.60  
  7 purchase totals = $1,140.82       $1,231.2224   $1,231.23   $1,231.20   $1,231.20