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 $226.33   8.476%   $245.5137   $245.51   $245.50   $245.50  
  Purchase #2 $40.53   7.679%   $43.6423   $43.64   $43.65   $43.60  
  Purchase #3 $92.38   11.522%   $103.024   $103.02   $103.00   $103.00  
  Purchase #4 $106.33   12.356%   $119.4681   $119.47   $119.45   $119.50  
  Purchase #5 $195.36   8.353%   $211.6784   $211.68   $211.70   $211.70  
  Purchase #6 $57.42   11.202%   $63.8522   $63.85   $63.85   $63.90  
  Purchase #7 $157.89   13.150%   $178.6525   $178.65   $178.65   $178.70  
  7 purchase totals = $876.24       $965.8312   $965.82   $965.80   $965.90