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 $208.59   9.741%   $228.9088   $228.91   $228.90   $228.90  
  Purchase #2 $60.33   4.502%   $63.0461   $63.05   $63.05   $63.00  
  Purchase #3 $55.68   3.543%   $57.6527   $57.65   $57.65   $57.70  
  Purchase #4 $122.97   8.595%   $133.5393   $133.54   $133.55   $133.50  
  Purchase #5 $189.59   5.337%   $199.7084   $199.71   $199.70   $199.70  
  Purchase #6 $226.95   8.309%   $245.8073   $245.81   $245.80   $245.80  
  Purchase #7 $119.26   13.269%   $135.0846   $135.08   $135.10   $135.10  
  7 purchase totals = $983.37       $1,063.7472   $1,063.75   $1,063.75   $1,063.70