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   11.826%   $102.3096   $102.31   $102.30   $102.30  
  Purchase #2 $97.85   4.216%   $101.9754   $101.98   $102.00   $102.00  
  Purchase #3 $14.74   12.785%   $16.6245   $16.62   $16.60   $16.60  
  Purchase #4 $131.96   12.161%   $148.0077   $148.01   $148.00   $148.00  
  Purchase #5 $171.54   6.742%   $183.1052   $183.11   $183.10   $183.10  
  Purchase #6 $193.76   9.256%   $211.6944   $211.69   $211.70   $211.70  
  Purchase #7 $237.32   4.457%   $247.8974   $247.90   $247.90   $247.90  
  7 purchase totals = $938.66       $1,011.6142   $1,011.62   $1,011.60   $1,011.60