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 $182.65   13.847%   $207.9415   $207.94   $207.95   $207.90  
  Purchase #2 $247.64   11.577%   $276.3093   $276.31   $276.30   $276.30  
  Purchase #3 $173.44   6.592%   $184.8732   $184.87   $184.85   $184.90  
  Purchase #4 $123.28   9.412%   $134.8831   $134.88   $134.90   $134.90  
  Purchase #5 $217.36   10.779%   $240.7892   $240.79   $240.80   $240.80  
  Purchase #6 $108.97   9.338%   $119.1456   $119.15   $119.15   $119.10  
  Purchase #7 $83.51   12.553%   $93.993   $93.99   $94.00   $94.00  
  7 purchase totals = $1,136.85       $1,257.9349   $1,257.93   $1,257.95   $1,257.90