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 $60.44   7.256%   $64.8255   $64.83   $64.85   $64.80  
  Purchase #2 $116.82   4.381%   $121.9379   $121.94   $121.95   $121.90  
  Purchase #3 $37.40   8.184%   $40.4608   $40.46   $40.45   $40.50  
  Purchase #4 $222.67   6.854%   $237.9318   $237.93   $237.95   $237.90  
  Purchase #5 $193.58   13.767%   $220.2302   $220.23   $220.25   $220.20  
  Purchase #6 $216.65   13.276%   $245.4125   $245.41   $245.40   $245.40  
  Purchase #7 $107.68   10.855%   $119.3687   $119.37   $119.35   $119.40  
  7 purchase totals = $955.24       $1,050.1674   $1,050.17   $1,050.20   $1,050.10