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 $48.84   10.655%   $54.0439   $54.04   $54.05   $54.00  
  Purchase #2 $99.77   8.215%   $107.9661   $107.97   $107.95   $108.00  
  Purchase #3 $63.43   3.413%   $65.5949   $65.59   $65.60   $65.60  
  Purchase #4 $133.97   4.419%   $139.8901   $139.89   $139.90   $139.90  
  Purchase #5 $242.59   12.702%   $273.4038   $273.40   $273.40   $273.40  
  Purchase #6 $53.70   12.868%   $60.6101   $60.61   $60.60   $60.60  
  Purchase #7 $230.62   6.862%   $246.4451   $246.45   $246.45   $246.40  
  7 purchase totals = $872.92       $947.9540   $947.95   $947.95   $947.90