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 $68.58   12.416%   $77.0949   $77.09   $77.10   $77.10  
  Purchase #2 $114.54   6.229%   $121.6747   $121.67   $121.65   $121.70  
  Purchase #3 $239.32   3.178%   $246.9256   $246.93   $246.95   $246.90  
  Purchase #4 $239.26   8.854%   $260.4441   $260.44   $260.45   $260.40  
  Purchase #5 $231.90   13.271%   $262.6754   $262.68   $262.70   $262.70  
  Purchase #6 $40.75   11.189%   $45.3095   $45.31   $45.30   $45.30  
  Purchase #7 $84.90   10.758%   $94.0335   $94.03   $94.05   $94.00  
  7 purchase totals = $1,019.25       $1,108.1577   $1,108.15   $1,108.20   $1,108.10