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 $212.62   11.136%   $236.2974   $236.30   $236.30   $236.30  
  Purchase #2 $162.74   12.745%   $183.4812   $183.48   $183.50   $183.50  
  Purchase #3 $76.50   7.634%   $82.34   $82.34   $82.35   $82.30  
  Purchase #4 $101.72   12.721%   $114.6598   $114.66   $114.65   $114.70  
  Purchase #5 $95.31   9.441%   $104.3082   $104.31   $104.30   $104.30  
  Purchase #6 $77.86   3.587%   $80.6528   $80.65   $80.65   $80.70  
  Purchase #7 $216.46   6.540%   $230.6165   $230.62   $230.60   $230.60  
  7 purchase totals = $943.21       $1,032.3559   $1,032.36   $1,032.35   $1,032.40