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 $93.67   11.163%   $104.1264   $104.13   $104.15   $104.10  
  Purchase #2 $217.38   6.783%   $232.1249   $232.12   $232.10   $232.10  
  Purchase #3 $111.47   6.803%   $119.0533   $119.05   $119.05   $119.10  
  Purchase #4 $156.40   11.826%   $174.8959   $174.90   $174.90   $174.90  
  Purchase #5 $62.28   9.612%   $68.2664   $68.27   $68.25   $68.30  
  Purchase #6 $167.25   8.575%   $181.5917   $181.59   $181.60   $181.60  
  Purchase #7 $134.99   4.690%   $141.321   $141.32   $141.30   $141.30  
  7 purchase totals = $943.44       $1,021.3796   $1,021.38   $1,021.35   $1,021.40