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 $239.70   12.451%   $269.545   $269.55   $269.55   $269.50  
  Purchase #2 $214.51   13.563%   $243.604   $243.60   $243.60   $243.60  
  Purchase #3 $158.58   5.533%   $167.3542   $167.35   $167.35   $167.40  
  Purchase #4 $89.75   4.534%   $93.8193   $93.82   $93.80   $93.80  
  Purchase #5 $79.39   7.621%   $85.4403   $85.44   $85.45   $85.40  
  Purchase #6 $121.78   5.309%   $128.2453   $128.25   $128.25   $128.20  
  Purchase #7 $214.57   13.370%   $243.258   $243.26   $243.25   $243.30  
  7 purchase totals = $1,118.28       $1,231.2661   $1,231.27   $1,231.25   $1,231.20