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 $92.27   4.871%   $96.7645   $96.76   $96.75   $96.80  
  Purchase #2 $218.31   4.500%   $228.134   $228.13   $228.15   $228.10  
  Purchase #3 $42.34   8.708%   $46.027   $46.03   $46.05   $46.00  
  Purchase #4 $93.48   6.860%   $99.8927   $99.89   $99.90   $99.90  
  Purchase #5 $202.65   10.866%   $224.6699   $224.67   $224.65   $224.70  
  Purchase #6 $31.37   10.293%   $34.5989   $34.60   $34.60   $34.60  
  Purchase #7 $116.33   6.152%   $123.4866   $123.49   $123.50   $123.50  
  7 purchase totals = $796.75       $853.5736   $853.57   $853.60   $853.60