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 $161.82   13.849%   $184.2305   $184.23   $184.25   $184.20  
  Purchase #2 $229.47   4.810%   $240.5075   $240.51   $240.50   $240.50  
  Purchase #3 $96.72   12.259%   $108.5769   $108.58   $108.60   $108.60  
  Purchase #4 $172.69   13.390%   $195.8132   $195.81   $195.80   $195.80  
  Purchase #5 $33.58   9.292%   $36.7003   $36.70   $36.70   $36.70  
  Purchase #6 $151.90   7.712%   $163.6145   $163.61   $163.60   $163.60  
  Purchase #7 $87.90   6.347%   $93.479   $93.48   $93.50   $93.50  
  7 purchase totals = $934.08       $1,022.9219   $1,022.92   $1,022.95   $1,022.90