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 $54.30   11.854%   $60.7367   $60.74   $60.75   $60.70  
  Purchase #2 $206.35   9.165%   $225.262   $225.26   $225.25   $225.30  
  Purchase #3 $235.36   4.339%   $245.5723   $245.57   $245.55   $245.60  
  Purchase #4 $76.68   10.189%   $84.4929   $84.49   $84.50   $84.50  
  Purchase #5 $20.74   11.409%   $23.1062   $23.11   $23.10   $23.10  
  Purchase #6 $87.46   9.752%   $95.9891   $95.99   $96.00   $96.00  
  Purchase #7 $235.32   13.513%   $267.1188   $267.12   $267.10   $267.10  
  7 purchase totals = $916.21       $1,002.2780   $1,002.28   $1,002.25   $1,002.30