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 $192.89   3.519%   $199.6778   $199.68   $199.70   $199.70  
  Purchase #2 $160.65   12.766%   $181.1586   $181.16   $181.15   $181.20  
  Purchase #3 $151.75   6.777%   $162.0341   $162.03   $162.05   $162.00  
  Purchase #4 $168.51   5.418%   $177.6399   $177.64   $177.65   $177.60  
  Purchase #5 $24.37   5.706%   $25.7606   $25.76   $25.75   $25.80  
  Purchase #6 $98.56   3.716%   $102.2225   $102.22   $102.20   $102.20  
  Purchase #7 $200.27   5.189%   $210.662   $210.66   $210.65   $210.70  
  7 purchase totals = $997.00       $1,059.1555   $1,059.15   $1,059.15   $1,059.20