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 $158.90   10.150%   $175.0284   $175.03   $175.05   $175.00  
  Purchase #2 $230.42   9.656%   $252.6694   $252.67   $252.65   $252.70  
  Purchase #3 $60.66   5.128%   $63.7706   $63.77   $63.75   $63.80  
  Purchase #4 $169.85   10.744%   $188.0987   $188.10   $188.10   $188.10  
  Purchase #5 $232.35   13.732%   $264.2563   $264.26   $264.25   $264.30  
  Purchase #6 $242.57   9.535%   $265.699   $265.70   $265.70   $265.70  
  Purchase #7 $210.56   11.722%   $235.2418   $235.24   $235.25   $235.20  
  7 purchase totals = $1,305.31       $1,444.7642   $1,444.77   $1,444.75   $1,444.80