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 $234.69   10.847%   $260.1468   $260.15   $260.15   $260.10  
  Purchase #2 $192.92   12.632%   $217.2897   $217.29   $217.30   $217.30  
  Purchase #3 $85.73   9.195%   $93.6129   $93.61   $93.60   $93.60  
  Purchase #4 $166.97   9.348%   $182.5784   $182.58   $182.60   $182.60  
  Purchase #5 $25.94   4.384%   $27.0772   $27.08   $27.10   $27.10  
  Purchase #6 $147.43   5.159%   $155.0359   $155.04   $155.05   $155.00  
  Purchase #7 $108.43   8.145%   $117.2616   $117.26   $117.25   $117.30  
  7 purchase totals = $962.11       $1,053.0025   $1,053.01   $1,053.05   $1,053.00