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 $104.34   5.353%   $109.9253   $109.93   $109.95   $109.90  
  Purchase #2 $58.76   4.774%   $61.5652   $61.57   $61.55   $61.60  
  Purchase #3 $124.79   9.776%   $136.9895   $136.99   $137.00   $137.00  
  Purchase #4 $101.76   11.457%   $113.4186   $113.42   $113.40   $113.40  
  Purchase #5 $41.67   12.724%   $46.9721   $46.97   $46.95   $47.00  
  Purchase #6 $91.39   3.587%   $94.6682   $94.67   $94.65   $94.70  
  Purchase #7 $181.85   4.383%   $189.8205   $189.82   $189.80   $189.80  
  7 purchase totals = $704.56       $753.3594   $753.37   $753.30   $753.40