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 $167.46   3.772%   $173.7766   $173.78   $173.80   $173.80  
  Purchase #2 $154.67   4.284%   $161.2961   $161.30   $161.30   $161.30  
  Purchase #3 $233.93   13.789%   $266.1866   $266.19   $266.20   $266.20  
  Purchase #4 $247.95   4.359%   $258.7581   $258.76   $258.75   $258.80  
  Purchase #5 $241.53   11.760%   $269.9339   $269.93   $269.95   $269.90  
  Purchase #6 $136.94   11.340%   $152.469   $152.47   $152.45   $152.50  
  Purchase #7 $212.53   11.516%   $237.005   $237.01   $237.00   $237.00  
  7 purchase totals = $1,395.01       $1,519.4253   $1,519.44   $1,519.45   $1,519.50