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 $15.79   8.193%   $17.0837   $17.08   $17.10   $17.10  
  Purchase #2 $171.70   9.180%   $187.4621   $187.46   $187.45   $187.50  
  Purchase #3 $226.25   10.698%   $250.4542   $250.45   $250.45   $250.50  
  Purchase #4 $68.56   10.617%   $75.839   $75.84   $75.85   $75.80  
  Purchase #5 $240.95   11.280%   $268.1292   $268.13   $268.15   $268.10  
  Purchase #6 $33.56   10.688%   $37.1469   $37.15   $37.15   $37.10  
  Purchase #7 $241.81   3.755%   $250.89   $250.89   $250.90   $250.90  
  7 purchase totals = $998.62       $1,087.0051   $1,087.00   $1,087.05   $1,087.00