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 $38.58   12.397%   $43.3628   $43.36   $43.35   $43.40  
  Purchase #2 $124.47   8.646%   $135.2317   $135.23   $135.25   $135.20  
  Purchase #3 $163.33   9.355%   $178.6095   $178.61   $178.60   $178.60  
  Purchase #4 $211.94   9.580%   $232.2439   $232.24   $232.25   $232.20  
  Purchase #5 $80.37   11.375%   $89.5121   $89.51   $89.50   $89.50  
  Purchase #6 $192.26   10.183%   $211.8378   $211.84   $211.85   $211.80  
  Purchase #7 $54.50   12.508%   $61.3169   $61.32   $61.30   $61.30  
  7 purchase totals = $865.45       $952.1147   $952.11   $952.10   $952.00