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 $211.43   11.512%   $235.7698   $235.77   $235.75   $235.80  
  Purchase #2 $114.92   12.508%   $129.2942   $129.29   $129.30   $129.30  
  Purchase #3 $121.37   10.475%   $134.0835   $134.08   $134.10   $134.10  
  Purchase #4 $11.88   8.285%   $12.8643   $12.86   $12.85   $12.90  
  Purchase #5 $241.96   3.857%   $251.2924   $251.29   $251.30   $251.30  
  Purchase #6 $23.95   3.311%   $24.743   $24.74   $24.75   $24.70  
  Purchase #7 $154.37   10.288%   $170.2516   $170.25   $170.25   $170.30  
  7 purchase totals = $879.88       $958.2988   $958.28   $958.30   $958.40