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 $24.71   4.270%   $25.7651   $25.77   $25.75   $25.80  
  Purchase #2 $32.55   9.644%   $35.6891   $35.69   $35.70   $35.70  
  Purchase #3 $170.38   5.615%   $179.9468   $179.95   $179.95   $179.90  
  Purchase #4 $249.70   12.587%   $281.1297   $281.13   $281.15   $281.10  
  Purchase #5 $243.30   6.745%   $259.7106   $259.71   $259.70   $259.70  
  Purchase #6 $155.93   3.650%   $161.6214   $161.62   $161.60   $161.60  
  Purchase #7 $121.50   3.373%   $125.5982   $125.60   $125.60   $125.60  
  7 purchase totals = $998.07       $1,069.4609   $1,069.47   $1,069.45   $1,069.40