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 $227.65   6.642%   $242.7705   $242.77   $242.75   $242.80  
  Purchase #2 $149.31   11.640%   $166.6897   $166.69   $166.70   $166.70  
  Purchase #3 $54.99   4.411%   $57.4156   $57.42   $57.40   $57.40  
  Purchase #4 $217.45   11.642%   $242.7655   $242.77   $242.75   $242.80  
  Purchase #5 $246.62   9.846%   $270.9022   $270.90   $270.90   $270.90  
  Purchase #6 $122.25   11.170%   $135.9053   $135.91   $135.90   $135.90  
  Purchase #7 $43.27   10.657%   $47.8813   $47.88   $47.90   $47.90  
  7 purchase totals = $1,061.54       $1,164.3301   $1,164.34   $1,164.30   $1,164.40