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 $74.36   13.533%   $84.4231   $84.42   $84.40   $84.40  
  Purchase #2 $215.89   10.703%   $238.9967   $239.00   $239.00   $239.00  
  Purchase #3 $34.28   9.629%   $37.5808   $37.58   $37.60   $37.60  
  Purchase #4 $186.36   4.380%   $194.5226   $194.52   $194.50   $194.50  
  Purchase #5 $121.33   12.158%   $136.0813   $136.08   $136.10   $136.10  
  Purchase #6 $194.44   8.107%   $210.2033   $210.20   $210.20   $210.20  
  Purchase #7 $156.65   5.549%   $165.3425   $165.34   $165.35   $165.30  
  7 purchase totals = $983.31       $1,067.1503   $1,067.14   $1,067.15   $1,067.10