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 $156.47   6.855%   $167.196   $167.20   $167.20   $167.20  
  Purchase #2 $59.56   6.751%   $63.5809   $63.58   $63.60   $63.60  
  Purchase #3 $242.54   10.554%   $268.1377   $268.14   $268.15   $268.10  
  Purchase #4 $160.87   12.712%   $181.3198   $181.32   $181.30   $181.30  
  Purchase #5 $220.68   8.839%   $240.1859   $240.19   $240.20   $240.20  
  Purchase #6 $117.76   10.285%   $129.8716   $129.87   $129.85   $129.90  
  Purchase #7 $95.59   10.508%   $105.6346   $105.63   $105.65   $105.60  
  7 purchase totals = $1,053.47       $1,155.9265   $1,155.93   $1,155.95   $1,155.90