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 $235.71   7.558%   $253.525   $253.53   $253.55   $253.50  
  Purchase #2 $32.27   10.479%   $35.6516   $35.65   $35.65   $35.70  
  Purchase #3 $246.26   13.317%   $279.0544   $279.05   $279.05   $279.10  
  Purchase #4 $51.74   9.591%   $56.7024   $56.70   $56.70   $56.70  
  Purchase #5 $124.38   12.408%   $139.8131   $139.81   $139.80   $139.80  
  Purchase #6 $11.34   8.483%   $12.302   $12.30   $12.30   $12.30  
  Purchase #7 $216.38   3.455%   $223.8559   $223.86   $223.85   $223.90  
  7 purchase totals = $918.08       $1,000.9044   $1,000.90   $1,000.90   $1,001.00