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 $57.55   6.702%   $61.407   $61.41   $61.40   $61.40  
  Purchase #2 $58.96   12.450%   $66.3005   $66.30   $66.30   $66.30  
  Purchase #3 $229.99   12.294%   $258.265   $258.27   $258.25   $258.30  
  Purchase #4 $161.45   12.764%   $182.0575   $182.06   $182.05   $182.10  
  Purchase #5 $129.27   8.873%   $140.7401   $140.74   $140.75   $140.70  
  Purchase #6 $231.45   10.560%   $255.8911   $255.89   $255.90   $255.90  
  Purchase #7 $124.35   3.460%   $128.6525   $128.65   $128.65   $128.70  
  7 purchase totals = $993.02       $1,093.3137   $1,093.32   $1,093.30   $1,093.40