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 $99.62   4.693%   $104.2952   $104.30   $104.30   $104.30  
  Purchase #2 $213.77   10.294%   $235.7755   $235.78   $235.80   $235.80  
  Purchase #3 $52.61   11.476%   $58.6475   $58.65   $58.65   $58.60  
  Purchase #4 $148.39   5.557%   $156.636   $156.64   $156.65   $156.60  
  Purchase #5 $34.53   4.423%   $36.0573   $36.06   $36.05   $36.10  
  Purchase #6 $228.25   4.133%   $237.6836   $237.68   $237.70   $237.70  
  Purchase #7 $170.32   4.243%   $177.5467   $177.55   $177.55   $177.50  
  7 purchase totals = $947.49       $1,006.6418   $1,006.66   $1,006.70   $1,006.60