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 $226.87   5.644%   $239.6745   $239.67   $239.65   $239.70  
  Purchase #2 $168.79   10.716%   $186.8775   $186.88   $186.90   $186.90  
  Purchase #3 $73.94   11.447%   $82.4039   $82.40   $82.40   $82.40  
  Purchase #4 $169.31   8.599%   $183.869   $183.87   $183.85   $183.90  
  Purchase #5 $198.49   6.178%   $210.7527   $210.75   $210.75   $210.80  
  Purchase #6 $120.29   7.813%   $129.6883   $129.69   $129.70   $129.70  
  Purchase #7 $54.25   12.612%   $61.092   $61.09   $61.10   $61.10  
  7 purchase totals = $1,011.94       $1,094.3579   $1,094.35   $1,094.35   $1,094.50