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 $44.72   11.103%   $49.6853   $49.69   $49.70   $49.70  
  Purchase #2 $59.78   5.821%   $63.2598   $63.26   $63.25   $63.30  
  Purchase #3 $175.29   13.184%   $198.4002   $198.40   $198.40   $198.40  
  Purchase #4 $250.63   7.335%   $269.0137   $269.01   $269.00   $269.00  
  Purchase #5 $23.85   8.263%   $25.8207   $25.82   $25.80   $25.80  
  Purchase #6 $95.67   12.469%   $107.5991   $107.60   $107.60   $107.60  
  Purchase #7 $7.91   7.665%   $8.5163   $8.52   $8.50   $8.50  
  7 purchase totals = $657.85       $722.2951   $722.30   $722.25   $722.30