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 $65.42   5.419%   $68.9651   $68.97   $68.95   $69.00  
  Purchase #2 $57.26   13.556%   $65.0222   $65.02   $65.00   $65.00  
  Purchase #3 $66.42   3.201%   $68.5461   $68.55   $68.55   $68.50  
  Purchase #4 $204.65   9.429%   $223.9464   $223.95   $223.95   $223.90  
  Purchase #5 $113.76   11.847%   $127.2371   $127.24   $127.25   $127.20  
  Purchase #6 $10.57   8.397%   $11.4576   $11.46   $11.45   $11.50  
  Purchase #7 $89.97   10.630%   $99.5338   $99.53   $99.55   $99.50  
  7 purchase totals = $608.05       $664.7083   $664.72   $664.70   $664.60