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 $55.80   9.786%   $61.2606   $61.26   $61.25   $61.30  
  Purchase #2 $133.94   8.158%   $144.8668   $144.87   $144.85   $144.90  
  Purchase #3 $193.34   9.392%   $211.4985   $211.50   $211.50   $211.50  
  Purchase #4 $135.60   3.728%   $140.6552   $140.66   $140.65   $140.70  
  Purchase #5 $221.91   7.252%   $238.0029   $238.00   $238.00   $238.00  
  Purchase #6 $178.31   8.457%   $193.3897   $193.39   $193.40   $193.40  
  Purchase #7 $18.34   13.837%   $20.8777   $20.88   $20.90   $20.90  
  7 purchase totals = $937.24       $1,010.5514   $1,010.56   $1,010.55   $1,010.70