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 $200.69   3.157%   $207.0258   $207.03   $207.05   $207.00  
  Purchase #2 $95.82   10.668%   $106.0421   $106.04   $106.05   $106.00  
  Purchase #3 $110.69   3.415%   $114.4701   $114.47   $114.45   $114.50  
  Purchase #4 $157.69   5.679%   $166.6452   $166.65   $166.65   $166.60  
  Purchase #5 $37.83   13.185%   $42.8179   $42.82   $42.80   $42.80  
  Purchase #6 $241.92   10.212%   $266.6249   $266.62   $266.60   $266.60  
  Purchase #7 $9.68   13.468%   $10.9837   $10.98   $11.00   $11.00  
  7 purchase totals = $854.32       $914.6097   $914.61   $914.60   $914.50