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 $190.81   6.397%   $203.0161   $203.02   $203.00   $203.00  
  Purchase #2 $134.96   13.315%   $152.9299   $152.93   $152.95   $152.90  
  Purchase #3 $112.76   6.680%   $120.2924   $120.29   $120.30   $120.30  
  Purchase #4 $160.74   11.218%   $178.7718   $178.77   $178.75   $178.80  
  Purchase #5 $213.48   9.303%   $233.34   $233.34   $233.35   $233.30  
  Purchase #6 $162.88   12.405%   $183.0853   $183.09   $183.10   $183.10  
  Purchase #7 $76.32   6.426%   $81.2243   $81.22   $81.20   $81.20  
  7 purchase totals = $1,051.95       $1,152.6598   $1,152.66   $1,152.65   $1,152.60