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 $224.52   13.589%   $255.03   $255.03   $255.05   $255.00  
  Purchase #2 $12.56   12.495%   $14.1294   $14.13   $14.15   $14.10  
  Purchase #3 $64.62   5.303%   $68.0468   $68.05   $68.05   $68.00  
  Purchase #4 $193.48   4.440%   $202.0705   $202.07   $202.05   $202.10  
  Purchase #5 $216.92   10.835%   $240.4233   $240.42   $240.40   $240.40  
  Purchase #6 $237.86   5.196%   $250.2192   $250.22   $250.20   $250.20  
  Purchase #7 $36.79   3.723%   $38.1597   $38.16   $38.15   $38.20  
  7 purchase totals = $986.75       $1,068.0789   $1,068.08   $1,068.05   $1,068.00