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 $78.39   8.696%   $85.2068   $85.21   $85.20   $85.20  
  Purchase #2 $217.96   11.872%   $243.8362   $243.84   $243.85   $243.80  
  Purchase #3 $85.91   4.755%   $89.995   $90.00   $90.00   $90.00  
  Purchase #4 $28.39   12.623%   $31.9737   $31.97   $31.95   $32.00  
  Purchase #5 $163.81   8.849%   $178.3055   $178.31   $178.30   $178.30  
  Purchase #6 $198.91   12.556%   $223.8851   $223.89   $223.90   $223.90  
  Purchase #7 $67.67   7.858%   $72.9875   $72.99   $73.00   $73.00  
  7 purchase totals = $841.04       $926.1898   $926.21   $926.20   $926.20