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 $86.65   7.154%   $92.8489   $92.85   $92.85   $92.80  
  Purchase #2 $208.60   6.533%   $222.2278   $222.23   $222.25   $222.20  
  Purchase #3 $148.41   5.297%   $156.2713   $156.27   $156.25   $156.30  
  Purchase #4 $218.63   6.239%   $232.2703   $232.27   $232.25   $232.30  
  Purchase #5 $218.29   12.249%   $245.0283   $245.03   $245.05   $245.00  
  Purchase #6 $245.94   5.557%   $259.6069   $259.61   $259.60   $259.60  
  Purchase #7 $111.90   9.278%   $122.2821   $122.28   $122.30   $122.30  
  7 purchase totals = $1,238.42       $1,330.5356   $1,330.54   $1,330.55   $1,330.50