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 $119.43   6.348%   $127.0114   $127.01   $127.00   $127.00  
  Purchase #2 $249.33   8.494%   $270.5081   $270.51   $270.50   $270.50  
  Purchase #3 $38.48   8.738%   $41.8424   $41.84   $41.85   $41.80  
  Purchase #4 $222.42   6.710%   $237.3444   $237.34   $237.35   $237.30  
  Purchase #5 $188.96   9.577%   $207.0567   $207.06   $207.05   $207.10  
  Purchase #6 $53.41   9.138%   $58.2906   $58.29   $58.30   $58.30  
  Purchase #7 $138.29   4.142%   $144.018   $144.02   $144.00   $144.00  
  7 purchase totals = $1,010.32       $1,086.0716   $1,086.07   $1,086.05   $1,086.00