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 $69.41   9.462%   $75.9776   $75.98   $76.00   $76.00  
  Purchase #2 $86.40   7.193%   $92.6148   $92.61   $92.60   $92.60  
  Purchase #3 $30.27   5.176%   $31.8368   $31.84   $31.85   $31.80  
  Purchase #4 $90.52   3.331%   $93.5352   $93.54   $93.55   $93.50  
  Purchase #5 $229.26   10.108%   $252.4336   $252.43   $252.45   $252.40  
  Purchase #6 $208.28   6.235%   $221.2663   $221.27   $221.25   $221.30  
  Purchase #7 $40.62   9.171%   $44.3453   $44.35   $44.35   $44.30  
  7 purchase totals = $754.76       $812.0096   $812.02   $812.05   $811.90