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 $158.58   11.601%   $176.9769   $176.98   $177.00   $177.00  
  Purchase #2 $191.54   7.523%   $205.9496   $205.95   $205.95   $205.90  
  Purchase #3 $118.90   13.765%   $135.2666   $135.27   $135.25   $135.30  
  Purchase #4 $120.31   9.585%   $131.8417   $131.84   $131.85   $131.80  
  Purchase #5 $7.62   3.689%   $7.9011   $7.90   $7.90   $7.90  
  Purchase #6 $49.99   10.784%   $55.3809   $55.38   $55.40   $55.40  
  Purchase #7 $10.77   8.617%   $11.6981   $11.70   $11.70   $11.70  
  7 purchase totals = $657.71       $725.0149   $725.02   $725.05   $725.00