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 $84.56   10.295%   $93.2655   $93.27   $93.25   $93.30  
  Purchase #2 $151.77   6.468%   $161.5865   $161.59   $161.60   $161.60  
  Purchase #3 $216.95   10.648%   $240.0508   $240.05   $240.05   $240.10  
  Purchase #4 $181.26   6.747%   $193.4896   $193.49   $193.50   $193.50  
  Purchase #5 $97.55   6.494%   $103.8849   $103.88   $103.90   $103.90  
  Purchase #6 $182.98   5.705%   $193.419   $193.42   $193.40   $193.40  
  Purchase #7 $23.56   12.318%   $26.4621   $26.46   $26.45   $26.50  
  7 purchase totals = $938.63       $1,012.1584   $1,012.16   $1,012.15   $1,012.30