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 $92.55   9.169%   $101.0359   $101.04   $101.05   $101.00  
  Purchase #2 $220.27   13.673%   $250.3875   $250.39   $250.40   $250.40  
  Purchase #3 $83.78   13.730%   $95.283   $95.28   $95.30   $95.30  
  Purchase #4 $158.43   13.202%   $179.3459   $179.35   $179.35   $179.30  
  Purchase #5 $203.37   10.569%   $224.8642   $224.86   $224.85   $224.90  
  Purchase #6 $235.45   11.591%   $262.741   $262.74   $262.75   $262.70  
  Purchase #7 $5.69   6.576%   $6.0642   $6.06   $6.05   $6.10  
  7 purchase totals = $999.54       $1,119.7217   $1,119.72   $1,119.75   $1,119.70