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 $108.48   11.253%   $120.6873   $120.69   $120.70   $120.70  
  Purchase #2 $30.88   13.697%   $35.1096   $35.11   $35.10   $35.10  
  Purchase #3 $167.56   12.654%   $188.763   $188.76   $188.75   $188.80  
  Purchase #4 $241.80   5.808%   $255.8437   $255.84   $255.85   $255.80  
  Purchase #5 $129.64   3.558%   $134.2526   $134.25   $134.25   $134.30  
  Purchase #6 $197.82   4.115%   $205.9603   $205.96   $205.95   $206.00  
  Purchase #7 $119.66   13.815%   $136.191   $136.19   $136.20   $136.20  
  7 purchase totals = $995.84       $1,076.8075   $1,076.80   $1,076.80   $1,076.90