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 $147.55   10.428%   $162.9365   $162.94   $162.95   $162.90  
  Purchase #2 $178.26   13.861%   $202.9686   $202.97   $202.95   $203.00  
  Purchase #3 $84.54   7.134%   $90.5711   $90.57   $90.55   $90.60  
  Purchase #4 $218.74   8.636%   $237.6304   $237.63   $237.65   $237.60  
  Purchase #5 $244.38   7.732%   $263.2755   $263.28   $263.30   $263.30  
  Purchase #6 $106.49   3.632%   $110.3577   $110.36   $110.35   $110.40  
  Purchase #7 $169.91   13.546%   $192.926   $192.93   $192.95   $192.90  
  7 purchase totals = $1,149.87       $1,260.6658   $1,260.68   $1,260.70   $1,260.70