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 $87.51   7.623%   $94.1809   $94.18   $94.20   $94.20  
  Purchase #2 $208.50   9.139%   $227.5548   $227.55   $227.55   $227.60  
  Purchase #3 $183.98   6.175%   $195.3408   $195.34   $195.35   $195.30  
  Purchase #4 $175.65   3.786%   $182.3001   $182.30   $182.30   $182.30  
  Purchase #5 $202.58   12.459%   $227.8194   $227.82   $227.80   $227.80  
  Purchase #6 $83.59   5.227%   $87.9592   $87.96   $87.95   $88.00  
  Purchase #7 $242.73   10.833%   $269.0249   $269.02   $269.00   $269.00  
  7 purchase totals = $1,184.54       $1,284.1801   $1,284.17   $1,284.15   $1,284.20