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 $192.94   7.215%   $206.8606   $206.86   $206.85   $206.90  
  Purchase #2 $233.81   4.718%   $244.8412   $244.84   $244.85   $244.80  
  Purchase #3 $107.88   8.726%   $117.2936   $117.29   $117.30   $117.30  
  Purchase #4 $184.31   13.374%   $208.9596   $208.96   $208.95   $209.00  
  Purchase #5 $157.87   11.864%   $176.5997   $176.60   $176.60   $176.60  
  Purchase #6 $145.94   5.820%   $154.4337   $154.43   $154.45   $154.40  
  Purchase #7 $220.72   6.728%   $235.57   $235.57   $235.55   $235.60  
  7 purchase totals = $1,243.47       $1,344.5584   $1,344.55   $1,344.55   $1,344.60