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 $154.93   8.868%   $168.6692   $168.67   $168.65   $168.70  
  Purchase #2 $200.92   5.241%   $211.4502   $211.45   $211.45   $211.50  
  Purchase #3 $45.53   13.482%   $51.6684   $51.67   $51.65   $51.70  
  Purchase #4 $96.99   5.628%   $102.4486   $102.45   $102.45   $102.40  
  Purchase #5 $151.42   3.553%   $156.8   $156.80   $156.80   $156.80  
  Purchase #6 $65.81   3.566%   $68.1568   $68.16   $68.15   $68.20  
  Purchase #7 $129.29   4.730%   $135.4054   $135.41   $135.40   $135.40  
  7 purchase totals = $844.89       $894.5986   $894.61   $894.55   $894.70