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 $122.83   8.481%   $133.2472   $133.25   $133.25   $133.20  
  Purchase #2 $194.80   12.568%   $219.2825   $219.28   $219.30   $219.30  
  Purchase #3 $115.70   8.688%   $125.752   $125.75   $125.75   $125.80  
  Purchase #4 $54.80   6.834%   $58.545   $58.55   $58.55   $58.50  
  Purchase #5 $40.47   8.661%   $43.9751   $43.98   $44.00   $44.00  
  Purchase #6 $168.88   13.651%   $191.9338   $191.93   $191.95   $191.90  
  Purchase #7 $247.58   13.838%   $281.8401   $281.84   $281.85   $281.80  
  7 purchase totals = $945.06       $1,054.5757   $1,054.58   $1,054.65   $1,054.50