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 $92.84   3.473%   $96.0643   $96.06   $96.05   $96.10  
  Purchase #2 $213.34   3.230%   $220.2309   $220.23   $220.25   $220.20  
  Purchase #3 $200.61   13.756%   $228.2059   $228.21   $228.20   $228.20  
  Purchase #4 $245.75   10.270%   $270.9885   $270.99   $271.00   $271.00  
  Purchase #5 $190.32   10.141%   $209.6204   $209.62   $209.60   $209.60  
  Purchase #6 $80.82   7.679%   $87.0262   $87.03   $87.05   $87.00  
  Purchase #7 $186.53   13.806%   $212.2823   $212.28   $212.30   $212.30  
  7 purchase totals = $1,210.21       $1,324.4185   $1,324.42   $1,324.45   $1,324.40