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 $147.46   9.685%   $161.7415   $161.74   $161.75   $161.70  
  Purchase #2 $127.26   7.517%   $136.8261   $136.83   $136.85   $136.80  
  Purchase #3 $84.56   3.398%   $87.4333   $87.43   $87.45   $87.40  
  Purchase #4 $172.77   10.324%   $190.6068   $190.61   $190.60   $190.60  
  Purchase #5 $26.95   10.858%   $29.8762   $29.88   $29.90   $29.90  
  Purchase #6 $227.32   3.276%   $234.767   $234.77   $234.75   $234.80  
  Purchase #7 $174.29   4.853%   $182.7483   $182.75   $182.75   $182.70  
  7 purchase totals = $960.61       $1,023.9992   $1,024.01   $1,024.05   $1,023.90