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 $206.34   8.796%   $224.4897   $224.49   $224.50   $224.50  
  Purchase #2 $148.75   11.316%   $165.5826   $165.58   $165.60   $165.60  
  Purchase #3 $196.77   6.601%   $209.7588   $209.76   $209.75   $209.80  
  Purchase #4 $95.43   11.622%   $106.5209   $106.52   $106.50   $106.50  
  Purchase #5 $248.49   4.620%   $259.9702   $259.97   $259.95   $260.00  
  Purchase #6 $8.52   11.869%   $9.5312   $9.53   $9.55   $9.50  
  Purchase #7 $65.68   11.149%   $73.0027   $73.00   $73.00   $73.00  
  7 purchase totals = $969.98       $1,048.8561   $1,048.85   $1,048.85   $1,048.90