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 $92.99   12.651%   $104.7542   $104.75   $104.75   $104.80  
  Purchase #2 $220.75   11.319%   $245.7367   $245.74   $245.75   $245.70  
  Purchase #3 $215.40   4.425%   $224.9315   $224.93   $224.95   $224.90  
  Purchase #4 $85.59   10.483%   $94.5624   $94.56   $94.55   $94.60  
  Purchase #5 $216.92   6.383%   $230.766   $230.77   $230.75   $230.80  
  Purchase #6 $104.70   12.565%   $117.8556   $117.86   $117.85   $117.90  
  Purchase #7 $178.48   6.235%   $189.6082   $189.61   $189.60   $189.60  
  7 purchase totals = $1,114.83       $1,208.2146   $1,208.22   $1,208.20   $1,208.30