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 $165.81   10.331%   $182.9398   $182.94   $182.95   $182.90  
  Purchase #2 $248.81   13.301%   $281.9042   $281.90   $281.90   $281.90  
  Purchase #3 $119.89   7.871%   $129.3265   $129.33   $129.35   $129.30  
  Purchase #4 $56.39   11.392%   $62.8139   $62.81   $62.80   $62.80  
  Purchase #5 $152.55   8.822%   $166.008   $166.01   $166.00   $166.00  
  Purchase #6 $184.61   5.822%   $195.358   $195.36   $195.35   $195.40  
  Purchase #7 $240.60   10.315%   $265.4179   $265.42   $265.40   $265.40  
  7 purchase totals = $1,168.66       $1,283.7683   $1,283.77   $1,283.75   $1,283.70