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 $49.84   12.242%   $55.9414   $55.94   $55.95   $55.90  
  Purchase #2 $73.61   4.362%   $76.8209   $76.82   $76.80   $76.80  
  Purchase #3 $81.36   12.858%   $91.8213   $91.82   $91.80   $91.80  
  Purchase #4 $74.85   11.769%   $83.6591   $83.66   $83.65   $83.70  
  Purchase #5 $198.29   5.196%   $208.5931   $208.59   $208.60   $208.60  
  Purchase #6 $208.27   13.318%   $236.0074   $236.01   $236.00   $236.00  
  Purchase #7 $244.75   13.835%   $278.6112   $278.61   $278.60   $278.60  
  7 purchase totals = $930.97       $1,031.4544   $1,031.45   $1,031.40   $1,031.40