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 $64.28   8.402%   $69.6808   $69.68   $69.70   $69.70  
  Purchase #2 $60.88   6.119%   $64.6052   $64.61   $64.60   $64.60  
  Purchase #3 $192.30   8.791%   $209.2051   $209.21   $209.20   $209.20  
  Purchase #4 $50.83   6.293%   $54.0287   $54.03   $54.05   $54.00  
  Purchase #5 $33.69   6.179%   $35.7717   $35.77   $35.75   $35.80  
  Purchase #6 $175.61   13.565%   $199.4315   $199.43   $199.45   $199.40  
  Purchase #7 $165.55   3.819%   $171.8724   $171.87   $171.85   $171.90  
  7 purchase totals = $743.14       $804.5954   $804.60   $804.60   $804.60