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 $61.61   6.212%   $65.4372   $65.44   $65.45   $65.40  
  Purchase #2 $102.27   9.583%   $112.0705   $112.07   $112.05   $112.10  
  Purchase #3 $201.52   3.742%   $209.0609   $209.06   $209.05   $209.10  
  Purchase #4 $181.32   5.649%   $191.5628   $191.56   $191.55   $191.60  
  Purchase #5 $110.30   4.704%   $115.4885   $115.49   $115.50   $115.50  
  Purchase #6 $12.88   10.644%   $14.2509   $14.25   $14.25   $14.30  
  Purchase #7 $84.76   3.532%   $87.7537   $87.75   $87.75   $87.80  
  7 purchase totals = $754.66       $795.6245   $795.62   $795.60   $795.80