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 $209.62   11.786%   $234.3258   $234.33   $234.35   $234.30  
  Purchase #2 $168.94   9.216%   $184.5095   $184.51   $184.50   $184.50  
  Purchase #3 $186.58   3.315%   $192.7651   $192.77   $192.75   $192.80  
  Purchase #4 $167.34   6.292%   $177.869   $177.87   $177.85   $177.90  
  Purchase #5 $148.66   10.608%   $164.4299   $164.43   $164.45   $164.40  
  Purchase #6 $154.55   9.733%   $169.5924   $169.59   $169.60   $169.60  
  Purchase #7 $47.26   7.211%   $50.6679   $50.67   $50.65   $50.70  
  7 purchase totals = $1,082.95       $1,174.1596   $1,174.17   $1,174.15   $1,174.20