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 $220.44   4.319%   $229.9608   $229.96   $229.95   $230.00  
  Purchase #2 $51.64   5.697%   $54.5819   $54.58   $54.60   $54.60  
  Purchase #3 $144.41   8.311%   $156.4119   $156.41   $156.40   $156.40  
  Purchase #4 $27.61   6.564%   $29.4223   $29.42   $29.40   $29.40  
  Purchase #5 $45.84   10.297%   $50.5601   $50.56   $50.55   $50.60  
  Purchase #6 $79.44   12.646%   $89.486   $89.49   $89.50   $89.50  
  Purchase #7 $61.44   6.808%   $65.6228   $65.62   $65.60   $65.60  
  7 purchase totals = $630.82       $676.0458   $676.04   $676.00   $676.10