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 $152.39   3.249%   $157.3412   $157.34   $157.35   $157.30  
  Purchase #2 $41.82   11.293%   $46.5427   $46.54   $46.55   $46.50  
  Purchase #3 $22.53   13.662%   $25.608   $25.61   $25.60   $25.60  
  Purchase #4 $30.79   12.790%   $34.728   $34.73   $34.75   $34.70  
  Purchase #5 $55.54   4.443%   $58.0076   $58.01   $58.00   $58.00  
  Purchase #6 $238.52   5.383%   $251.3595   $251.36   $251.35   $251.40  
  Purchase #7 $159.49   12.268%   $179.0562   $179.06   $179.05   $179.10  
  7 purchase totals = $701.08       $752.6432   $752.65   $752.65   $752.60