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 $203.83   11.215%   $226.6895   $226.69   $226.70   $226.70  
  Purchase #2 $228.77   4.709%   $239.5428   $239.54   $239.55   $239.50  
  Purchase #3 $43.87   12.147%   $49.1989   $49.20   $49.20   $49.20  
  Purchase #4 $95.69   5.532%   $100.9836   $100.98   $101.00   $101.00  
  Purchase #5 $213.61   7.757%   $230.1797   $230.18   $230.20   $230.20  
  Purchase #6 $168.85   7.146%   $180.916   $180.92   $180.90   $180.90  
  Purchase #7 $160.59   3.464%   $166.1528   $166.15   $166.15   $166.20  
  7 purchase totals = $1,115.21       $1,193.6633   $1,193.66   $1,193.70   $1,193.70