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 $166.27   7.649%   $178.988   $178.99   $179.00   $179.00  
  Purchase #2 $236.65   12.221%   $265.571   $265.57   $265.55   $265.60  
  Purchase #3 $26.64   11.341%   $29.6612   $29.66   $29.65   $29.70  
  Purchase #4 $240.25   8.540%   $260.7674   $260.77   $260.75   $260.80  
  Purchase #5 $206.69   11.462%   $230.3808   $230.38   $230.40   $230.40  
  Purchase #6 $116.26   6.305%   $123.5902   $123.59   $123.60   $123.60  
  Purchase #7 $164.36   8.501%   $178.3322   $178.33   $178.35   $178.30  
  7 purchase totals = $1,157.12       $1,267.2908   $1,267.29   $1,267.30   $1,267.40