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 $56.34   13.378%   $63.8772   $63.88   $63.90   $63.90  
  Purchase #2 $155.44   7.471%   $167.0529   $167.05   $167.05   $167.10  
  Purchase #3 $176.62   3.741%   $183.2274   $183.23   $183.25   $183.20  
  Purchase #4 $99.52   13.872%   $113.3254   $113.33   $113.35   $113.30  
  Purchase #5 $201.40   11.463%   $224.4865   $224.49   $224.50   $224.50  
  Purchase #6 $239.56   5.525%   $252.7957   $252.80   $252.80   $252.80  
  Purchase #7 $48.47   8.532%   $52.6055   $52.61   $52.60   $52.60  
  7 purchase totals = $977.35       $1,057.3706   $1,057.39   $1,057.45   $1,057.40