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 $66.33   4.587%   $69.3726   $69.37   $69.35   $69.40  
  Purchase #2 $215.62   8.697%   $234.3725   $234.37   $234.35   $234.40  
  Purchase #3 $179.95   3.107%   $185.541   $185.54   $185.55   $185.50  
  Purchase #4 $187.28   3.152%   $193.1831   $193.18   $193.20   $193.20  
  Purchase #5 $87.40   10.135%   $96.258   $96.26   $96.25   $96.30  
  Purchase #6 $61.59   3.663%   $63.846   $63.85   $63.85   $63.80  
  Purchase #7 $169.83   5.204%   $178.668   $178.67   $178.65   $178.70  
  7 purchase totals = $968.00       $1,021.2412   $1,021.24   $1,021.20   $1,021.30