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 $226.95   11.411%   $252.8473   $252.85   $252.85   $252.80  
  Purchase #2 $114.27   9.163%   $124.7406   $124.74   $124.75   $124.70  
  Purchase #3 $72.50   7.425%   $77.8831   $77.88   $77.90   $77.90  
  Purchase #4 $208.71   3.862%   $216.7704   $216.77   $216.75   $216.80  
  Purchase #5 $54.97   6.360%   $58.4661   $58.47   $58.45   $58.50  
  Purchase #6 $218.93   4.380%   $228.5191   $228.52   $228.50   $228.50  
  Purchase #7 $129.78   7.171%   $139.0865   $139.09   $139.10   $139.10  
  7 purchase totals = $1,026.11       $1,098.3131   $1,098.32   $1,098.30   $1,098.30