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 $179.39   8.526%   $194.6848   $194.68   $194.70   $194.70  
  Purchase #2 $137.84   11.762%   $154.0527   $154.05   $154.05   $154.10  
  Purchase #3 $201.37   4.562%   $210.5565   $210.56   $210.55   $210.60  
  Purchase #4 $134.76   5.423%   $142.068   $142.07   $142.05   $142.10  
  Purchase #5 $132.46   8.614%   $143.8701   $143.87   $143.85   $143.90  
  Purchase #6 $142.37   6.735%   $151.9586   $151.96   $151.95   $152.00  
  Purchase #7 $25.88   7.770%   $27.8909   $27.89   $27.90   $27.90  
  7 purchase totals = $954.07       $1,025.0816   $1,025.08   $1,025.05   $1,025.30