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 $206.57   8.710%   $224.5622   $224.56   $224.55   $224.60  
  Purchase #2 $36.29   8.407%   $39.3409   $39.34   $39.35   $39.30  
  Purchase #3 $121.48   10.852%   $134.663   $134.66   $134.65   $134.70  
  Purchase #4 $78.98   4.796%   $82.7679   $82.77   $82.75   $82.80  
  Purchase #5 $218.69   7.514%   $235.1224   $235.12   $235.10   $235.10  
  Purchase #6 $176.92   5.306%   $186.3074   $186.31   $186.30   $186.30  
  Purchase #7 $95.29   12.134%   $106.8525   $106.85   $106.85   $106.90  
  7 purchase totals = $934.22       $1,009.6163   $1,009.61   $1,009.55   $1,009.70