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 $62.82   11.226%   $69.8722   $69.87   $69.85   $69.90  
  Purchase #2 $194.57   10.398%   $214.8014   $214.80   $214.80   $214.80  
  Purchase #3 $27.54   7.183%   $29.5182   $29.52   $29.50   $29.50  
  Purchase #4 $32.37   9.537%   $35.4571   $35.46   $35.45   $35.50  
  Purchase #5 $169.82   6.524%   $180.8991   $180.90   $180.90   $180.90  
  Purchase #6 $204.90   5.610%   $216.3949   $216.39   $216.40   $216.40  
  Purchase #7 $213.91   11.862%   $239.284   $239.28   $239.30   $239.30  
  7 purchase totals = $905.93       $986.2269   $986.22   $986.20   $986.30