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 $232.81   11.280%   $259.071   $259.07   $259.05   $259.10  
  Purchase #2 $12.81   9.426%   $14.0175   $14.02   $14.00   $14.00  
  Purchase #3 $235.33   10.607%   $260.2915   $260.29   $260.30   $260.30  
  Purchase #4 $129.54   3.436%   $133.991   $133.99   $134.00   $134.00  
  Purchase #5 $51.54   12.428%   $57.9454   $57.95   $57.95   $57.90  
  Purchase #6 $199.90   10.526%   $220.9415   $220.94   $220.95   $220.90  
  Purchase #7 $68.96   4.229%   $71.8763   $71.88   $71.90   $71.90  
  7 purchase totals = $930.89       $1,018.1342   $1,018.14   $1,018.15   $1,018.10