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 $68.94   11.644%   $76.9674   $76.97   $76.95   $77.00  
  Purchase #2 $215.46   8.865%   $234.5605   $234.56   $234.55   $234.60  
  Purchase #3 $57.74   9.647%   $63.3102   $63.31   $63.30   $63.30  
  Purchase #4 $115.77   6.453%   $123.2406   $123.24   $123.25   $123.20  
  Purchase #5 $179.70   3.560%   $186.0973   $186.10   $186.10   $186.10  
  Purchase #6 $150.96   5.108%   $158.671   $158.67   $158.65   $158.70  
  Purchase #7 $7.51   3.532%   $7.7753   $7.78   $7.80   $7.80  
  7 purchase totals = $796.08       $850.6223   $850.63   $850.60   $850.70