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 $84.58   12.702%   $95.3234   $95.32   $95.30   $95.30  
  Purchase #2 $59.41   4.305%   $61.9676   $61.97   $61.95   $62.00  
  Purchase #3 $56.88   11.771%   $63.5753   $63.58   $63.60   $63.60  
  Purchase #4 $139.70   10.538%   $154.4216   $154.42   $154.40   $154.40  
  Purchase #5 $185.85   8.338%   $201.3462   $201.35   $201.35   $201.30  
  Purchase #6 $25.43   12.647%   $28.6461   $28.65   $28.65   $28.60  
  Purchase #7 $217.28   11.236%   $241.6936   $241.69   $241.70   $241.70  
  7 purchase totals = $769.13       $846.9738   $846.98   $846.95   $846.90