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 $228.91   7.168%   $245.3183   $245.32   $245.30   $245.30  
  Purchase #2 $197.79   5.442%   $208.5537   $208.55   $208.55   $208.60  
  Purchase #3 $246.56   4.156%   $256.807   $256.81   $256.80   $256.80  
  Purchase #4 $129.83   11.599%   $144.889   $144.89   $144.90   $144.90  
  Purchase #5 $56.48   11.726%   $63.1028   $63.10   $63.10   $63.10  
  Purchase #6 $90.29   4.863%   $94.6808   $94.68   $94.70   $94.70  
  Purchase #7 $26.89   4.409%   $28.0756   $28.08   $28.10   $28.10  
  7 purchase totals = $976.75       $1,041.4272   $1,041.43   $1,041.45   $1,041.50