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 $65.61   6.485%   $69.8648   $69.86   $69.85   $69.90  
  Purchase #2 $122.94   11.136%   $136.6306   $136.63   $136.65   $136.60  
  Purchase #3 $210.61   12.314%   $236.5445   $236.54   $236.55   $236.50  
  Purchase #4 $133.91   12.539%   $150.701   $150.70   $150.70   $150.70  
  Purchase #5 $43.63   12.479%   $49.0746   $49.07   $49.05   $49.10  
  Purchase #6 $44.43   6.667%   $47.3921   $47.39   $47.40   $47.40  
  Purchase #7 $75.86   6.640%   $80.8971   $80.90   $80.90   $80.90  
  7 purchase totals = $696.99       $771.1047   $771.09   $771.10   $771.10