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 $61.47   10.376%   $67.8481   $67.85   $67.85   $67.80  
  Purchase #2 $23.26   7.274%   $24.9519   $24.95   $24.95   $25.00  
  Purchase #3 $36.50   10.107%   $40.1891   $40.19   $40.20   $40.20  
  Purchase #4 $180.98   7.874%   $195.2304   $195.23   $195.25   $195.20  
  Purchase #5 $179.29   11.273%   $199.5014   $199.50   $199.50   $199.50  
  Purchase #6 $235.47   12.600%   $265.1392   $265.14   $265.15   $265.10  
  Purchase #7 $199.48   7.745%   $214.9297   $214.93   $214.95   $214.90  
  7 purchase totals = $916.45       $1,007.7898   $1,007.79   $1,007.85   $1,007.70