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 $134.83   12.248%   $151.344   $151.34   $151.35   $151.30  
  Purchase #2 $62.57   11.652%   $69.8607   $69.86   $69.85   $69.90  
  Purchase #3 $81.49   10.619%   $90.1434   $90.14   $90.15   $90.10  
  Purchase #4 $216.29   4.861%   $226.8039   $226.80   $226.80   $226.80  
  Purchase #5 $149.71   9.182%   $163.4564   $163.46   $163.45   $163.50  
  Purchase #6 $233.59   13.495%   $265.113   $265.11   $265.10   $265.10  
  Purchase #7 $73.79   10.294%   $81.3859   $81.39   $81.40   $81.40  
  7 purchase totals = $952.27       $1,048.1073   $1,048.10   $1,048.10   $1,048.10