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 $167.68   11.674%   $187.255   $187.26   $187.25   $187.30  
  Purchase #2 $119.91   8.285%   $129.8445   $129.84   $129.85   $129.80  
  Purchase #3 $136.82   8.788%   $148.8437   $148.84   $148.85   $148.80  
  Purchase #4 $143.90   12.138%   $161.3666   $161.37   $161.35   $161.40  
  Purchase #5 $150.27   6.144%   $159.5026   $159.50   $159.50   $159.50  
  Purchase #6 $166.63   10.293%   $183.7812   $183.78   $183.80   $183.80  
  Purchase #7 $82.72   13.766%   $94.1072   $94.11   $94.10   $94.10  
  7 purchase totals = $967.93       $1,064.7008   $1,064.70   $1,064.70   $1,064.70