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 $239.49   12.337%   $269.0359   $269.04   $269.05   $269.00  
  Purchase #2 $121.94   8.137%   $131.8623   $131.86   $131.85   $131.90  
  Purchase #3 $62.43   12.865%   $70.4616   $70.46   $70.45   $70.50  
  Purchase #4 $56.83   6.843%   $60.7189   $60.72   $60.70   $60.70  
  Purchase #5 $212.83   12.598%   $239.6423   $239.64   $239.65   $239.60  
  Purchase #6 $119.87   4.237%   $124.9489   $124.95   $124.95   $124.90  
  Purchase #7 $167.29   3.251%   $172.7286   $172.73   $172.75   $172.70  
  7 purchase totals = $980.68       $1,069.3985   $1,069.40   $1,069.40   $1,069.30