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 $241.66   10.633%   $267.3557   $267.36   $267.35   $267.40  
  Purchase #2 $24.33   9.787%   $26.7112   $26.71   $26.70   $26.70  
  Purchase #3 $117.90   11.807%   $131.8205   $131.82   $131.80   $131.80  
  Purchase #4 $184.43   10.303%   $203.4318   $203.43   $203.45   $203.40  
  Purchase #5 $206.45   3.270%   $213.2009   $213.20   $213.20   $213.20  
  Purchase #6 $155.84   13.729%   $177.2353   $177.24   $177.25   $177.20  
  Purchase #7 $44.80   8.358%   $48.5444   $48.54   $48.55   $48.50  
  7 purchase totals = $975.41       $1,068.2998   $1,068.30   $1,068.30   $1,068.20