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 $42.66   13.809%   $48.5509   $48.55   $48.55   $48.60  
  Purchase #2 $89.99   4.470%   $94.0126   $94.01   $94.00   $94.00  
  Purchase #3 $33.60   3.593%   $34.8072   $34.81   $34.80   $34.80  
  Purchase #4 $24.65   11.282%   $27.431   $27.43   $27.45   $27.40  
  Purchase #5 $250.40   6.191%   $265.9023   $265.90   $265.90   $265.90  
  Purchase #6 $168.92   4.586%   $176.6667   $176.67   $176.65   $176.70  
  Purchase #7 $193.31   9.176%   $211.0481   $211.05   $211.05   $211.00  
  7 purchase totals = $803.53       $858.4188   $858.42   $858.40   $858.40