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 $23.68   8.495%   $25.6916   $25.69   $25.70   $25.70  
  Purchase #2 $153.26   6.139%   $162.6686   $162.67   $162.65   $162.70  
  Purchase #3 $70.75   12.654%   $79.7027   $79.70   $79.70   $79.70  
  Purchase #4 $55.54   6.188%   $58.9768   $58.98   $59.00   $59.00  
  Purchase #5 $234.56   7.824%   $252.912   $252.91   $252.90   $252.90  
  Purchase #6 $176.87   10.190%   $194.8931   $194.89   $194.90   $194.90  
  Purchase #7 $44.74   12.572%   $50.3647   $50.36   $50.35   $50.40  
  7 purchase totals = $759.40       $825.2095   $825.20   $825.20   $825.30