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 $179.82   13.176%   $203.5131   $203.51   $203.50   $203.50  
  Purchase #2 $29.68   12.377%   $33.3535   $33.35   $33.35   $33.40  
  Purchase #3 $109.99   9.784%   $120.7514   $120.75   $120.75   $120.80  
  Purchase #4 $200.80   5.618%   $212.0809   $212.08   $212.10   $212.10  
  Purchase #5 $175.42   4.141%   $182.6841   $182.68   $182.70   $182.70  
  Purchase #6 $87.92   9.250%   $96.0526   $96.05   $96.05   $96.10  
  Purchase #7 $209.45   4.464%   $218.7998   $218.80   $218.80   $218.80  
  7 purchase totals = $993.08       $1,067.2354   $1,067.22   $1,067.25   $1,067.40