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 $57.65   6.145%   $61.1926   $61.19   $61.20   $61.20  
  Purchase #2 $118.36   7.314%   $127.0169   $127.02   $127.00   $127.00  
  Purchase #3 $177.83   6.848%   $190.0078   $190.01   $190.00   $190.00  
  Purchase #4 $54.84   12.630%   $61.7663   $61.77   $61.75   $61.80  
  Purchase #5 $235.34   4.513%   $245.9609   $245.96   $245.95   $246.00  
  Purchase #6 $66.43   12.849%   $74.9656   $74.97   $74.95   $75.00  
  Purchase #7 $228.43   8.734%   $248.3811   $248.38   $248.40   $248.40  
  7 purchase totals = $938.88       $1,009.2912   $1,009.30   $1,009.25   $1,009.40