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 $39.65   13.394%   $44.9607   $44.96   $44.95   $45.00  
  Purchase #2 $222.78   12.853%   $251.4139   $251.41   $251.40   $251.40  
  Purchase #3 $156.59   10.440%   $172.938   $172.94   $172.95   $172.90  
  Purchase #4 $50.83   13.648%   $57.7673   $57.77   $57.75   $57.80  
  Purchase #5 $182.66   9.222%   $199.5049   $199.50   $199.50   $199.50  
  Purchase #6 $172.93   5.619%   $182.6469   $182.65   $182.65   $182.60  
  Purchase #7 $86.80   7.215%   $93.0626   $93.06   $93.05   $93.10  
  7 purchase totals = $912.24       $1,002.2943   $1,002.29   $1,002.25   $1,002.30