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 $91.49   6.585%   $97.5146   $97.51   $97.50   $97.50  
  Purchase #2 $128.72   4.841%   $134.9513   $134.95   $134.95   $135.00  
  Purchase #3 $167.40   11.182%   $186.1187   $186.12   $186.10   $186.10  
  Purchase #4 $66.36   4.710%   $69.4856   $69.49   $69.50   $69.50  
  Purchase #5 $113.74   11.602%   $126.9361   $126.94   $126.95   $126.90  
  Purchase #6 $228.34   5.663%   $241.2709   $241.27   $241.25   $241.30  
  Purchase #7 $45.37   10.514%   $50.1402   $50.14   $50.15   $50.10  
  7 purchase totals = $841.42       $906.4174   $906.42   $906.40   $906.40