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 $197.53   9.812%   $216.9116   $216.91   $216.90   $216.90  
  Purchase #2 $69.25   3.286%   $71.5256   $71.53   $71.55   $71.50  
  Purchase #3 $41.86   4.243%   $43.6361   $43.64   $43.65   $43.60  
  Purchase #4 $63.70   3.155%   $65.7097   $65.71   $65.70   $65.70  
  Purchase #5 $208.86   9.116%   $227.8997   $227.90   $227.90   $227.90  
  Purchase #6 $103.76   6.444%   $110.4463   $110.45   $110.45   $110.40  
  Purchase #7 $53.33   10.345%   $58.847   $58.85   $58.85   $58.80  
  7 purchase totals = $738.29       $794.9760   $794.99   $795.00   $794.80