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 $24.35   6.613%   $25.9603   $25.96   $25.95   $26.00  
  Purchase #2 $232.94   8.611%   $252.9985   $253.00   $253.00   $253.00  
  Purchase #3 $138.34   9.232%   $151.1115   $151.11   $151.10   $151.10  
  Purchase #4 $61.62   6.680%   $65.7362   $65.74   $65.75   $65.70  
  Purchase #5 $143.97   5.166%   $151.4075   $151.41   $151.40   $151.40  
  Purchase #6 $19.34   3.577%   $20.0318   $20.03   $20.05   $20.00  
  Purchase #7 $33.54   10.545%   $37.0768   $37.08   $37.10   $37.10  
  7 purchase totals = $654.10       $704.3226   $704.33   $704.35   $704.30