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 $14.39   13.509%   $16.3339   $16.33   $16.35   $16.30  
  Purchase #2 $208.82   13.184%   $236.3508   $236.35   $236.35   $236.40  
  Purchase #3 $190.72   13.557%   $216.5759   $216.58   $216.60   $216.60  
  Purchase #4 $214.98   4.146%   $223.8931   $223.89   $223.90   $223.90  
  Purchase #5 $110.73   6.471%   $117.8953   $117.90   $117.90   $117.90  
  Purchase #6 $194.95   7.577%   $209.7214   $209.72   $209.70   $209.70  
  Purchase #7 $47.81   9.803%   $52.4968   $52.50   $52.50   $52.50  
  7 purchase totals = $982.40       $1,073.2672   $1,073.27   $1,073.30   $1,073.30