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 $53.60   12.272%   $60.1778   $60.18   $60.20   $60.20  
  Purchase #2 $236.91   8.738%   $257.6112   $257.61   $257.60   $257.60  
  Purchase #3 $128.82   4.615%   $134.765   $134.77   $134.75   $134.80  
  Purchase #4 $108.65   4.843%   $113.9119   $113.91   $113.90   $113.90  
  Purchase #5 $143.61   6.735%   $153.2821   $153.28   $153.30   $153.30  
  Purchase #6 $185.67   8.573%   $201.5875   $201.59   $201.60   $201.60  
  Purchase #7 $69.61   5.271%   $73.2791   $73.28   $73.30   $73.30  
  7 purchase totals = $926.87       $994.6146   $994.62   $994.65   $994.70