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 $11.88   3.706%   $12.3203   $12.32   $12.30   $12.30  
  Purchase #2 $119.65   10.847%   $132.6284   $132.63   $132.65   $132.60  
  Purchase #3 $77.35   3.529%   $80.0797   $80.08   $80.10   $80.10  
  Purchase #4 $216.27   6.355%   $230.014   $230.01   $230.00   $230.00  
  Purchase #5 $248.40   4.446%   $259.4439   $259.44   $259.45   $259.40  
  Purchase #6 $61.64   11.612%   $68.7976   $68.80   $68.80   $68.80  
  Purchase #7 $11.64   13.781%   $13.2441   $13.24   $13.25   $13.20  
  7 purchase totals = $746.83       $796.5280   $796.52   $796.55   $796.40