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 $68.92   11.267%   $76.6852   $76.69   $76.70   $76.70  
  Purchase #2 $87.39   12.800%   $98.5759   $98.58   $98.60   $98.60  
  Purchase #3 $173.70   3.420%   $179.6405   $179.64   $179.65   $179.60  
  Purchase #4 $220.52   12.322%   $247.6925   $247.69   $247.70   $247.70  
  Purchase #5 $176.27   11.684%   $196.8654   $196.87   $196.85   $196.90  
  Purchase #6 $151.72   6.384%   $161.4058   $161.41   $161.40   $161.40  
  Purchase #7 $120.70   9.517%   $132.187   $132.19   $132.20   $132.20  
  7 purchase totals = $999.22       $1,093.0523   $1,093.07   $1,093.10   $1,093.10