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 $111.28   13.331%   $126.1147   $126.11   $126.10   $126.10  
  Purchase #2 $165.28   12.853%   $186.5234   $186.52   $186.50   $186.50  
  Purchase #3 $185.48   8.678%   $201.576   $201.58   $201.60   $201.60  
  Purchase #4 $22.42   11.691%   $25.0411   $25.04   $25.05   $25.00  
  Purchase #5 $86.55   11.735%   $96.7066   $96.71   $96.70   $96.70  
  Purchase #6 $249.44   6.845%   $266.5142   $266.51   $266.50   $266.50  
  Purchase #7 $245.53   9.604%   $269.1107   $269.11   $269.10   $269.10  
  7 purchase totals = $1,065.98       $1,171.5867   $1,171.58   $1,171.55   $1,171.50