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 $218.71   9.620%   $239.7499   $239.75   $239.75   $239.70  
  Purchase #2 $144.27   8.542%   $156.5935   $156.59   $156.60   $156.60  
  Purchase #3 $192.38   12.111%   $215.6791   $215.68   $215.70   $215.70  
  Purchase #4 $24.36   6.499%   $25.9432   $25.94   $25.95   $25.90  
  Purchase #5 $178.85   7.505%   $192.2727   $192.27   $192.25   $192.30  
  Purchase #6 $39.44   10.415%   $43.5477   $43.55   $43.55   $43.50  
  Purchase #7 $200.87   11.247%   $223.4618   $223.46   $223.45   $223.50  
  7 purchase totals = $998.88       $1,097.2479   $1,097.24   $1,097.25   $1,097.20