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 $228.26   11.600%   $254.7382   $254.74   $254.75   $254.70  
  Purchase #2 $131.57   3.183%   $135.7579   $135.76   $135.75   $135.80  
  Purchase #3 $98.97   9.271%   $108.1455   $108.15   $108.15   $108.10  
  Purchase #4 $208.55   8.402%   $226.0724   $226.07   $226.05   $226.10  
  Purchase #5 $189.93   6.590%   $202.4464   $202.45   $202.45   $202.40  
  Purchase #6 $89.79   5.688%   $94.8973   $94.90   $94.90   $94.90  
  Purchase #7 $69.29   4.714%   $72.5563   $72.56   $72.55   $72.60  
  7 purchase totals = $1,016.36       $1,094.6140   $1,094.63   $1,094.60   $1,094.60