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 $30.76   6.144%   $32.6499   $32.65   $32.65   $32.60  
  Purchase #2 $240.72   10.836%   $266.8044   $266.80   $266.80   $266.80  
  Purchase #3 $134.27   12.136%   $150.565   $150.57   $150.55   $150.60  
  Purchase #4 $70.39   13.200%   $79.6815   $79.68   $79.70   $79.70  
  Purchase #5 $113.30   6.212%   $120.3382   $120.34   $120.35   $120.30  
  Purchase #6 $201.72   5.540%   $212.8953   $212.90   $212.90   $212.90  
  Purchase #7 $117.78   5.401%   $124.1413   $124.14   $124.15   $124.10  
  7 purchase totals = $908.94       $987.0756   $987.08   $987.10   $987.00