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 $56.28   9.483%   $61.617   $61.62   $61.60   $61.60  
  Purchase #2 $79.61   6.675%   $84.924   $84.92   $84.90   $84.90  
  Purchase #3 $36.59   7.671%   $39.3968   $39.40   $39.40   $39.40  
  Purchase #4 $202.56   7.261%   $217.2679   $217.27   $217.25   $217.30  
  Purchase #5 $13.25   3.549%   $13.7202   $13.72   $13.70   $13.70  
  Purchase #6 $37.77   11.150%   $41.9814   $41.98   $42.00   $42.00  
  Purchase #7 $134.82   12.779%   $152.0486   $152.05   $152.05   $152.00  
  7 purchase totals = $560.88       $610.9559   $610.96   $610.90   $610.90