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 $50.34   11.700%   $56.2298   $56.23   $56.25   $56.20  
  Purchase #2 $248.67   7.107%   $266.343   $266.34   $266.35   $266.30  
  Purchase #3 $117.34   5.365%   $123.6353   $123.64   $123.65   $123.60  
  Purchase #4 $246.95   12.394%   $277.557   $277.56   $277.55   $277.60  
  Purchase #5 $50.38   13.466%   $57.1642   $57.16   $57.15   $57.20  
  Purchase #6 $236.93   3.341%   $244.8458   $244.85   $244.85   $244.80  
  Purchase #7 $179.49   7.831%   $193.5459   $193.55   $193.55   $193.50  
  7 purchase totals = $1,130.10       $1,219.3210   $1,219.33   $1,219.35   $1,219.20