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 $152.44   10.212%   $168.0072   $168.01   $168.00   $168.00  
  Purchase #2 $203.83   13.156%   $230.6459   $230.65   $230.65   $230.60  
  Purchase #3 $17.33   10.776%   $19.1975   $19.20   $19.20   $19.20  
  Purchase #4 $210.51   8.405%   $228.2034   $228.20   $228.20   $228.20  
  Purchase #5 $27.26   10.556%   $30.1376   $30.14   $30.15   $30.10  
  Purchase #6 $248.56   13.187%   $281.3376   $281.34   $281.35   $281.30  
  Purchase #7 $95.56   12.864%   $107.8528   $107.85   $107.85   $107.90  
  7 purchase totals = $955.49       $1,065.3820   $1,065.39   $1,065.40   $1,065.30