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 $165.90   12.273%   $186.2609   $186.26   $186.25   $186.30  
  Purchase #2 $109.55   10.774%   $121.3529   $121.35   $121.35   $121.40  
  Purchase #3 $101.75   5.493%   $107.3391   $107.34   $107.35   $107.30  
  Purchase #4 $230.61   4.476%   $240.9321   $240.93   $240.95   $240.90  
  Purchase #5 $235.67   8.124%   $254.8158   $254.82   $254.80   $254.80  
  Purchase #6 $84.65   10.675%   $93.6864   $93.69   $93.70   $93.70  
  Purchase #7 $36.64   8.189%   $39.6404   $39.64   $39.65   $39.60  
  7 purchase totals = $964.77       $1,044.0276   $1,044.03   $1,044.05   $1,044.00