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 $101.94   4.716%   $106.7475   $106.75   $106.75   $106.70  
  Purchase #2 $8.81   11.866%   $9.8554   $9.86   $9.85   $9.90  
  Purchase #3 $50.69   5.586%   $53.5215   $53.52   $53.50   $53.50  
  Purchase #4 $68.98   3.653%   $71.4998   $71.50   $71.50   $71.50  
  Purchase #5 $115.57   7.264%   $123.965   $123.97   $123.95   $124.00  
  Purchase #6 $176.89   4.325%   $184.5405   $184.54   $184.55   $184.50  
  Purchase #7 $223.85   8.443%   $242.7497   $242.75   $242.75   $242.70  
  7 purchase totals = $746.73       $792.8794   $792.89   $792.85   $792.80