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 $208.42   10.816%   $230.9627   $230.96   $230.95   $231.00  
  Purchase #2 $240.58   7.535%   $258.7077   $258.71   $258.70   $258.70  
  Purchase #3 $232.97   6.535%   $248.1946   $248.19   $248.20   $248.20  
  Purchase #4 $5.82   9.335%   $6.3633   $6.36   $6.35   $6.40  
  Purchase #5 $93.91   10.311%   $103.5931   $103.59   $103.60   $103.60  
  Purchase #6 $52.65   13.351%   $59.6793   $59.68   $59.70   $59.70  
  Purchase #7 $246.92   10.213%   $272.1379   $272.14   $272.15   $272.10  
  7 purchase totals = $1,081.27       $1,179.6386   $1,179.63   $1,179.65   $1,179.70