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 $143.37   6.680%   $152.9471   $152.95   $152.95   $152.90  
  Purchase #2 $197.82   12.712%   $222.9669   $222.97   $222.95   $223.00  
  Purchase #3 $160.47   9.795%   $176.188   $176.19   $176.20   $176.20  
  Purchase #4 $157.48   6.203%   $167.2485   $167.25   $167.25   $167.20  
  Purchase #5 $165.34   9.169%   $180.5   $180.50   $180.50   $180.50  
  Purchase #6 $127.75   9.280%   $139.6052   $139.61   $139.60   $139.60  
  Purchase #7 $43.44   12.721%   $48.966   $48.97   $48.95   $49.00  
  7 purchase totals = $995.67       $1,088.4217   $1,088.44   $1,088.40   $1,088.40