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 $56.87   13.283%   $64.424   $64.42   $64.40   $64.40  
  Purchase #2 $194.59   3.584%   $201.5641   $201.56   $201.55   $201.60  
  Purchase #3 $7.39   5.772%   $7.8166   $7.82   $7.80   $7.80  
  Purchase #4 $208.63   5.703%   $220.5282   $220.53   $220.55   $220.50  
  Purchase #5 $190.64   6.433%   $202.9039   $202.90   $202.90   $202.90  
  Purchase #6 $249.52   3.321%   $257.8066   $257.81   $257.80   $257.80  
  Purchase #7 $57.27   6.573%   $61.0344   $61.03   $61.05   $61.00  
  7 purchase totals = $964.91       $1,016.0778   $1,016.07   $1,016.05   $1,016.00