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 $234.26   5.314%   $246.7086   $246.71   $246.70   $246.70  
  Purchase #2 $49.97   12.575%   $56.2537   $56.25   $56.25   $56.30  
  Purchase #3 $65.65   4.446%   $68.5688   $68.57   $68.55   $68.60  
  Purchase #4 $215.95   11.604%   $241.0088   $241.01   $241.00   $241.00  
  Purchase #5 $114.31   7.867%   $123.3028   $123.30   $123.30   $123.30  
  Purchase #6 $144.75   6.359%   $153.9547   $153.95   $153.95   $154.00  
  Purchase #7 $241.29   13.357%   $273.5191   $273.52   $273.50   $273.50  
  7 purchase totals = $1,066.18       $1,163.3165   $1,163.31   $1,163.25   $1,163.40