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 $90.62   4.557%   $94.7496   $94.75   $94.75   $94.70  
  Purchase #2 $129.34   6.444%   $137.6747   $137.67   $137.65   $137.70  
  Purchase #3 $125.39   13.288%   $142.0518   $142.05   $142.05   $142.10  
  Purchase #4 $89.44   6.688%   $95.4217   $95.42   $95.40   $95.40  
  Purchase #5 $198.25   10.227%   $218.525   $218.53   $218.55   $218.50  
  Purchase #6 $242.94   3.723%   $251.9847   $251.98   $252.00   $252.00  
  Purchase #7 $81.27   5.660%   $85.8699   $85.87   $85.85   $85.90  
  7 purchase totals = $957.25       $1,026.2774   $1,026.27   $1,026.25   $1,026.30