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 $239.28   7.677%   $257.6495   $257.65   $257.65   $257.60  
  Purchase #2 $110.31   11.353%   $122.8335   $122.83   $122.85   $122.80  
  Purchase #3 $245.76   7.704%   $264.6934   $264.69   $264.70   $264.70  
  Purchase #4 $37.26   3.493%   $38.5615   $38.56   $38.55   $38.60  
  Purchase #5 $31.29   9.796%   $34.3552   $34.36   $34.35   $34.40  
  Purchase #6 $127.79   13.740%   $145.3483   $145.35   $145.35   $145.30  
  Purchase #7 $98.58   13.135%   $111.5285   $111.53   $111.55   $111.50  
  7 purchase totals = $890.27       $974.9699   $974.97   $975.00   $974.90