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 $150.91   8.433%   $163.6362   $163.64   $163.65   $163.60  
  Purchase #2 $93.53   11.163%   $103.9708   $103.97   $103.95   $104.00  
  Purchase #3 $105.71   9.773%   $116.041   $116.04   $116.05   $116.00  
  Purchase #4 $167.33   11.840%   $187.1419   $187.14   $187.15   $187.10  
  Purchase #5 $38.64   8.697%   $42.0005   $42.00   $42.00   $42.00  
  Purchase #6 $208.43   13.695%   $236.9745   $236.97   $236.95   $237.00  
  Purchase #7 $218.45   12.186%   $245.0703   $245.07   $245.05   $245.10  
  7 purchase totals = $983.00       $1,094.8352   $1,094.83   $1,094.80   $1,094.80