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 $34.99   10.259%   $38.5796   $38.58   $38.60   $38.60  
  Purchase #2 $180.43   12.764%   $203.4601   $203.46   $203.45   $203.50  
  Purchase #3 $59.68   7.609%   $64.2211   $64.22   $64.20   $64.20  
  Purchase #4 $231.47   9.720%   $253.9689   $253.97   $253.95   $254.00  
  Purchase #5 $177.97   10.572%   $196.785   $196.79   $196.80   $196.80  
  Purchase #6 $142.45   13.629%   $161.8645   $161.86   $161.85   $161.90  
  Purchase #7 $202.42   6.291%   $215.1542   $215.15   $215.15   $215.20  
  7 purchase totals = $1,029.41       $1,134.0334   $1,134.03   $1,134.00   $1,134.20