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 $241.77   11.470%   $269.501   $269.50   $269.50   $269.50  
  Purchase #2 $53.60   7.371%   $57.5509   $57.55   $57.55   $57.60  
  Purchase #3 $238.52   11.401%   $265.7137   $265.71   $265.70   $265.70  
  Purchase #4 $244.67   9.254%   $267.3118   $267.31   $267.30   $267.30  
  Purchase #5 $143.94   9.139%   $157.0947   $157.09   $157.10   $157.10  
  Purchase #6 $211.89   9.691%   $232.4243   $232.42   $232.40   $232.40  
  Purchase #7 $105.63   13.153%   $119.5235   $119.52   $119.50   $119.50  
  7 purchase totals = $1,240.02       $1,369.1199   $1,369.10   $1,369.05   $1,369.10