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 $107.26   11.600%   $119.7022   $119.70   $119.70   $119.70  
  Purchase #2 $196.61   7.607%   $211.5661   $211.57   $211.55   $211.60  
  Purchase #3 $56.39   8.327%   $61.0856   $61.09   $61.10   $61.10  
  Purchase #4 $241.70   12.759%   $272.5385   $272.54   $272.55   $272.50  
  Purchase #5 $151.69   5.119%   $159.455   $159.46   $159.45   $159.50  
  Purchase #6 $106.75   13.235%   $120.8784   $120.88   $120.90   $120.90  
  Purchase #7 $238.49   7.521%   $256.4268   $256.43   $256.45   $256.40  
  7 purchase totals = $1,098.89       $1,201.6526   $1,201.67   $1,201.70   $1,201.70