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 $65.46   5.542%   $69.0878   $69.09   $69.10   $69.10  
  Purchase #2 $241.59   3.620%   $250.3356   $250.34   $250.35   $250.30  
  Purchase #3 $13.92   4.193%   $14.5037   $14.50   $14.50   $14.50  
  Purchase #4 $229.52   7.362%   $246.4173   $246.42   $246.40   $246.40  
  Purchase #5 $208.58   13.113%   $235.9311   $235.93   $235.95   $235.90  
  Purchase #6 $30.49   7.415%   $32.7508   $32.75   $32.75   $32.80  
  Purchase #7 $131.31   8.529%   $142.5094   $142.51   $142.50   $142.50  
  7 purchase totals = $920.87       $991.5357   $991.54   $991.55   $991.50