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 $243.39   10.633%   $269.2697   $269.27   $269.25   $269.30  
  Purchase #2 $39.42   10.871%   $43.7053   $43.71   $43.70   $43.70  
  Purchase #3 $138.66   3.387%   $143.3564   $143.36   $143.35   $143.40  
  Purchase #4 $125.53   10.243%   $138.388   $138.39   $138.40   $138.40  
  Purchase #5 $163.42   11.224%   $181.7623   $181.76   $181.75   $181.80  
  Purchase #6 $140.96   12.757%   $158.9423   $158.94   $158.95   $158.90  
  Purchase #7 $13.57   9.553%   $14.8663   $14.87   $14.85   $14.90  
  7 purchase totals = $864.95       $950.2903   $950.30   $950.25   $950.40