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 $194.93   8.580%   $211.655   $211.66   $211.65   $211.70  
  Purchase #2 $71.81   12.308%   $80.6484   $80.65   $80.65   $80.60  
  Purchase #3 $118.99   3.606%   $123.2808   $123.28   $123.30   $123.30  
  Purchase #4 $57.26   7.469%   $61.5367   $61.54   $61.55   $61.50  
  Purchase #5 $226.34   10.156%   $249.3271   $249.33   $249.35   $249.30  
  Purchase #6 $51.56   8.698%   $56.0447   $56.04   $56.05   $56.00  
  Purchase #7 $156.28   7.728%   $168.3573   $168.36   $168.35   $168.40  
  7 purchase totals = $877.17       $950.8500   $950.86   $950.90   $950.80