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 $56.34   7.765%   $60.7148   $60.71   $60.70   $60.70  
  Purchase #2 $85.75   8.263%   $92.8355   $92.84   $92.85   $92.80  
  Purchase #3 $10.25   12.737%   $11.5555   $11.56   $11.55   $11.60  
  Purchase #4 $194.95   5.255%   $205.1946   $205.19   $205.20   $205.20  
  Purchase #5 $210.88   12.190%   $236.5863   $236.59   $236.60   $236.60  
  Purchase #6 $172.90   6.247%   $183.7011   $183.70   $183.70   $183.70  
  Purchase #7 $33.51   8.186%   $36.2531   $36.25   $36.25   $36.30  
  7 purchase totals = $764.58       $826.8409   $826.84   $826.85   $826.90