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 $58.97   4.124%   $61.4019   $61.40   $61.40   $61.40  
  Purchase #2 $136.80   9.343%   $149.5812   $149.58   $149.60   $149.60  
  Purchase #3 $23.94   11.534%   $26.7012   $26.70   $26.70   $26.70  
  Purchase #4 $237.70   6.447%   $253.0245   $253.02   $253.00   $253.00  
  Purchase #5 $235.72   11.413%   $262.6227   $262.62   $262.60   $262.60  
  Purchase #6 $45.68   10.154%   $50.3183   $50.32   $50.30   $50.30  
  Purchase #7 $165.93   7.787%   $178.851   $178.85   $178.85   $178.90  
  7 purchase totals = $904.74       $982.5008   $982.49   $982.45   $982.50