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 $45.34   11.777%   $50.6797   $50.68   $50.70   $50.70  
  Purchase #2 $112.78   8.838%   $122.7475   $122.75   $122.75   $122.70  
  Purchase #3 $222.91   10.314%   $245.9009   $245.90   $245.90   $245.90  
  Purchase #4 $33.72   10.721%   $37.3351   $37.34   $37.35   $37.30  
  Purchase #5 $235.34   5.549%   $248.399   $248.40   $248.40   $248.40  
  Purchase #6 $228.77   5.652%   $241.7001   $241.70   $241.70   $241.70  
  Purchase #7 $145.78   12.249%   $163.6366   $163.64   $163.65   $163.60  
  7 purchase totals = $1,024.64       $1,110.3989   $1,110.41   $1,110.45   $1,110.30