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 $61.91   11.627%   $69.1083   $69.11   $69.10   $69.10  
  Purchase #2 $41.56   7.340%   $44.6105   $44.61   $44.60   $44.60  
  Purchase #3 $42.66   7.741%   $45.9623   $45.96   $45.95   $46.00  
  Purchase #4 $150.32   11.459%   $167.5452   $167.55   $167.55   $167.50  
  Purchase #5 $146.63   7.597%   $157.7695   $157.77   $157.75   $157.80  
  Purchase #6 $244.40   7.680%   $263.1699   $263.17   $263.15   $263.20  
  Purchase #7 $212.30   6.745%   $226.6196   $226.62   $226.60   $226.60  
  7 purchase totals = $899.78       $974.7853   $974.79   $974.70   $974.80