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 $92.62   12.245%   $103.9613   $103.96   $103.95   $104.00  
  Purchase #2 $178.88   12.183%   $200.673   $200.67   $200.65   $200.70  
  Purchase #3 $16.96   11.439%   $18.9001   $18.90   $18.90   $18.90  
  Purchase #4 $213.63   8.131%   $231.0003   $231.00   $231.00   $231.00  
  Purchase #5 $196.68   9.491%   $215.3469   $215.35   $215.35   $215.30  
  Purchase #6 $214.53   8.284%   $232.3017   $232.30   $232.30   $232.30  
  Purchase #7 $171.93   4.185%   $179.1253   $179.13   $179.15   $179.10  
  7 purchase totals = $1,085.23       $1,181.3086   $1,181.31   $1,181.30   $1,181.30