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 $97.26   10.827%   $107.7903   $107.79   $107.80   $107.80  
  Purchase #2 $138.27   13.751%   $157.2835   $157.28   $157.30   $157.30  
  Purchase #3 $124.27   4.458%   $129.81   $129.81   $129.80   $129.80  
  Purchase #4 $203.37   6.372%   $216.3287   $216.33   $216.35   $216.30  
  Purchase #5 $80.75   4.761%   $84.5945   $84.59   $84.60   $84.60  
  Purchase #6 $40.58   8.670%   $44.0983   $44.10   $44.10   $44.10  
  Purchase #7 $122.26   3.405%   $126.423   $126.42   $126.40   $126.40  
  7 purchase totals = $806.76       $866.3283   $866.32   $866.35   $866.30