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 $198.54   10.306%   $219.0015   $219.00   $219.00   $219.00  
  Purchase #2 $82.77   7.181%   $88.7137   $88.71   $88.70   $88.70  
  Purchase #3 $149.89   7.646%   $161.3506   $161.35   $161.35   $161.40  
  Purchase #4 $213.81   6.419%   $227.5345   $227.53   $227.55   $227.50  
  Purchase #5 $188.77   4.685%   $197.6139   $197.61   $197.60   $197.60  
  Purchase #6 $248.68   6.330%   $264.4214   $264.42   $264.40   $264.40  
  Purchase #7 $40.50   7.692%   $43.6153   $43.62   $43.60   $43.60  
  7 purchase totals = $1,122.96       $1,202.2509   $1,202.24   $1,202.20   $1,202.20