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 $67.95   13.691%   $77.253   $77.25   $77.25   $77.30  
  Purchase #2 $103.43   11.532%   $115.3575   $115.36   $115.35   $115.40  
  Purchase #3 $87.49   4.431%   $91.3667   $91.37   $91.35   $91.40  
  Purchase #4 $55.39   5.307%   $58.3295   $58.33   $58.35   $58.30  
  Purchase #5 $223.56   8.149%   $241.7779   $241.78   $241.80   $241.80  
  Purchase #6 $144.71   9.144%   $157.9423   $157.94   $157.95   $157.90  
  Purchase #7 $141.52   10.786%   $156.7843   $156.78   $156.80   $156.80  
  7 purchase totals = $824.05       $898.8112   $898.81   $898.85   $898.90