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 $62.49   3.798%   $64.8634   $64.86   $64.85   $64.90  
  Purchase #2 $32.41   7.337%   $34.7879   $34.79   $34.80   $34.80  
  Purchase #3 $183.74   5.416%   $193.6914   $193.69   $193.70   $193.70  
  Purchase #4 $242.35   12.842%   $273.4726   $273.47   $273.45   $273.50  
  Purchase #5 $195.59   7.305%   $209.8778   $209.88   $209.90   $209.90  
  Purchase #6 $66.63   12.252%   $74.7935   $74.79   $74.80   $74.80  
  Purchase #7 $124.90   4.496%   $130.5155   $130.52   $130.50   $130.50  
  7 purchase totals = $908.11       $982.0021   $982.00   $982.00   $982.10