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 $54.95   12.187%   $61.6468   $61.65   $61.65   $61.60  
  Purchase #2 $9.85   13.140%   $11.1443   $11.14   $11.15   $11.10  
  Purchase #3 $118.56   11.848%   $132.607   $132.61   $132.60   $132.60  
  Purchase #4 $46.77   12.550%   $52.6396   $52.64   $52.65   $52.60  
  Purchase #5 $27.94   9.365%   $30.5566   $30.56   $30.55   $30.60  
  Purchase #6 $141.31   7.557%   $151.9888   $151.99   $152.00   $152.00  
  Purchase #7 $221.56   5.580%   $233.923   $233.92   $233.90   $233.90  
  7 purchase totals = $620.94       $674.5061   $674.51   $674.50   $674.40