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 $59.58   6.789%   $63.6249   $63.62   $63.60   $63.60  
  Purchase #2 $59.84   13.758%   $68.0728   $68.07   $68.05   $68.10  
  Purchase #3 $43.76   11.213%   $48.6668   $48.67   $48.65   $48.70  
  Purchase #4 $44.96   6.251%   $47.7704   $47.77   $47.75   $47.80  
  Purchase #5 $212.68   12.283%   $238.8035   $238.80   $238.80   $238.80  
  Purchase #6 $138.97   5.730%   $146.933   $146.93   $146.95   $146.90  
  Purchase #7 $8.82   11.442%   $9.8292   $9.83   $9.85   $9.80  
  7 purchase totals = $568.61       $623.7006   $623.69   $623.65   $623.70