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 $62.29   13.414%   $70.6456   $70.65   $70.65   $70.60  
  Purchase #2 $22.46   7.288%   $24.0969   $24.10   $24.10   $24.10  
  Purchase #3 $63.79   11.246%   $70.9638   $70.96   $70.95   $71.00  
  Purchase #4 $163.34   11.861%   $182.7138   $182.71   $182.70   $182.70  
  Purchase #5 $45.57   11.489%   $50.8055   $50.81   $50.80   $50.80  
  Purchase #6 $230.52   6.758%   $246.0985   $246.10   $246.10   $246.10  
  Purchase #7 $21.96   5.750%   $23.2227   $23.22   $23.20   $23.20  
  7 purchase totals = $609.93       $668.5468   $668.55   $668.50   $668.50