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 $83.77   10.705%   $92.7376   $92.74   $92.75   $92.70  
  Purchase #2 $218.95   5.820%   $231.6929   $231.69   $231.70   $231.70  
  Purchase #3 $243.98   9.323%   $266.7263   $266.73   $266.75   $266.70  
  Purchase #4 $177.87   8.831%   $193.5777   $193.58   $193.60   $193.60  
  Purchase #5 $118.33   10.827%   $131.1416   $131.14   $131.15   $131.10  
  Purchase #6 $215.27   12.266%   $241.675   $241.68   $241.70   $241.70  
  Purchase #7 $162.53   7.187%   $174.211   $174.21   $174.20   $174.20  
  7 purchase totals = $1,220.70       $1,331.7621   $1,331.77   $1,331.85   $1,331.70