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 $211.86   13.643%   $240.7641   $240.76   $240.75   $240.80  
  Purchase #2 $52.55   3.699%   $54.4938   $54.49   $54.50   $54.50  
  Purchase #3 $243.90   11.703%   $272.4436   $272.44   $272.45   $272.40  
  Purchase #4 $58.65   10.682%   $64.915   $64.92   $64.90   $64.90  
  Purchase #5 $229.36   12.809%   $258.7387   $258.74   $258.75   $258.70  
  Purchase #6 $197.91   13.633%   $224.8911   $224.89   $224.90   $224.90  
  Purchase #7 $37.40   9.436%   $40.9291   $40.93   $40.95   $40.90  
  7 purchase totals = $1,031.63       $1,157.1754   $1,157.17   $1,157.20   $1,157.10