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 $52.86   10.791%   $58.5641   $58.56   $58.55   $58.60  
  Purchase #2 $114.52   13.598%   $130.0924   $130.09   $130.10   $130.10  
  Purchase #3 $132.54   4.492%   $138.4937   $138.49   $138.50   $138.50  
  Purchase #4 $190.83   4.578%   $199.5662   $199.57   $199.55   $199.60  
  Purchase #5 $70.70   7.226%   $75.8088   $75.81   $75.80   $75.80  
  Purchase #6 $195.69   5.646%   $206.7387   $206.74   $206.75   $206.70  
  Purchase #7 $183.34   10.252%   $202.136   $202.14   $202.15   $202.10  
  7 purchase totals = $940.48       $1,011.3999   $1,011.40   $1,011.40   $1,011.40