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 $82.36   11.625%   $91.9344   $91.93   $91.95   $91.90  
  Purchase #2 $121.33   10.445%   $134.0029   $134.00   $134.00   $134.00  
  Purchase #3 $75.80   3.376%   $78.359   $78.36   $78.35   $78.40  
  Purchase #4 $106.44   10.814%   $117.9504   $117.95   $117.95   $118.00  
  Purchase #5 $216.76   7.652%   $233.3465   $233.35   $233.35   $233.30  
  Purchase #6 $156.42   6.801%   $167.0581   $167.06   $167.05   $167.10  
  Purchase #7 $173.47   5.463%   $182.9467   $182.95   $182.95   $182.90  
  7 purchase totals = $932.58       $1,005.5980   $1,005.60   $1,005.60   $1,005.60