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 $215.74   13.672%   $245.236   $245.24   $245.25   $245.20  
  Purchase #2 $27.80   5.608%   $29.359   $29.36   $29.35   $29.40  
  Purchase #3 $241.92   5.659%   $255.6103   $255.61   $255.60   $255.60  
  Purchase #4 $213.49   6.667%   $227.7234   $227.72   $227.70   $227.70  
  Purchase #5 $24.98   12.114%   $28.0061   $28.01   $28.00   $28.00  
  Purchase #6 $142.74   9.227%   $155.9106   $155.91   $155.90   $155.90  
  Purchase #7 $53.98   8.295%   $58.4576   $58.46   $58.45   $58.50  
  7 purchase totals = $920.65       $1,000.3030   $1,000.31   $1,000.25   $1,000.30