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 $41.82   6.597%   $44.5789   $44.58   $44.60   $44.60  
  Purchase #2 $113.80   13.113%   $128.7226   $128.72   $128.70   $128.70  
  Purchase #3 $203.67   4.610%   $213.0592   $213.06   $213.05   $213.10  
  Purchase #4 $232.40   5.674%   $245.5864   $245.59   $245.60   $245.60  
  Purchase #5 $202.29   11.413%   $225.3774   $225.38   $225.40   $225.40  
  Purchase #6 $199.54   11.209%   $221.9064   $221.91   $221.90   $221.90  
  Purchase #7 $142.80   3.186%   $147.3496   $147.35   $147.35   $147.30  
  7 purchase totals = $1,136.32       $1,226.5805   $1,226.59   $1,226.60   $1,226.60